From b2a2d804e9ccf72714ef3b7549425bfb6a61a2b1 Mon Sep 17 00:00:00 2001
From: ChristianGruen <ChristianGruen@users.noreply.github.com>
Date: Thu, 9 Jan 2025 12:06:07 +0000
Subject: [PATCH] =?UTF-8?q?Deploying=20to=20gh-pages=20from=20@=20qt4cg/qt?=
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 <h1>Index</h1>
-<p>Published 09 Jan 2025 at 11:55:21 +0000.</p>
+<p>Published 09 Jan 2025 at 12:03:08 +0000.</p>
 <ul>
 <li><a href='xslt-xquery-serialization-40/Overview.html'>xslt-xquery-serialization-40</a></li>
 <li><a href='xquery-40/xpath-40.html'>xpath-40</a></li>
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 let $f := function($a) { $a mod 2 = 0 }
 return local:filter(1 to 10, $f)</pre></div></div><p>Here the supplied function <code>$f</code> is an instance of the required type, because its signature defaults the argument type to <code>item()*</code>, which is a supertype of <code>xs:string</code>. The expression <code>$s[$p(.)]</code> could in principle succeed. However, function coercion ensures that the supplied function is wrapped in a function that requires the argument to be of type <code>xs:string</code>, so the call fails with a type error when the wrapping function is invoked supplying an <code>xs:integer</code> as the argument.</p><div class="xquery"><p class="xquery">This has the consequence that in XQuery 4.0, there is a backwards incompatibility introduced because coercion rules now apply to global variable declarations (<code>declare variable</code>) and local variable bindings (for example <code>let</code> clauses). Previously the following would execute without error:</p></div><div class="xquery"><div class="exampleInner"><pre xml:space="preserve">let $f as function(xs:integer) as item()* := function($x) { $x + 1 }
-return $f(12.3)</pre></div></div><div class="xquery"><p class="xquery">With XQuery 4.0, as a consequence of function coercion, this fails with a type error because the argument supplied in the function call is not of type <code>xs:integer</code>.</p></div></div></div><div class="div3"><h4><a id="id-coercion-examples"></a>3.4.5 Examples of Coercions</h4><p>This section illustrates the effect of the coercion rules with examples.</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-string"></a>Example: Coercion to <code>xs:string</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:string</code>. For example, the second argument of <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-matches"><code>fn:matches</code></a>, which expects a regular expression. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><div class="medium"><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>"[0-9]"</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>default-language()</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of <code>xs:language</code>, which is a subtype of the required type <code>xs:string</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;[0-9]&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. Unless it has been schema-validated, the typed value will be an instance of <code>xs:untypedAtomic</code>, which is accepted when the required type is <code>xs:string</code>.</p><p>Supplying an element whose type annotation is (say) <code>xs:date</code> will fail with a type error.</p><div class="xpath"><p class="xpath">The effect is subtly different if XPath 1.0 compatibility mode is enabled. In this case coercion takes the string value of the element node. This differs from the typed value only in the case where the element has been schema-validated and has a type annotation other than <code>xs:string</code>.</p></div></td></tr><tr><td style="vertical-align:top"><code>xs:anyURI("urn:dummy")</code></td><td style="vertical-align:top"><p>Supplying an instance of <code>xs:anyURI</code> where the expected type is <code>xs:string</code> is permitted; this is one of the pairs of types where implicit casting is allowed.</p></td></tr><tr class="xpath"><td style="vertical-align:top"><code>17.2</code></td><td style="vertical-align:top"><p>Supplying a number where a string is expected raises a type error.</p><div class="xpath"><p class="xpath">However, if XPath 1.0 compatibility mode is enabled, the number is converted to a string as if by the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-string"><code>fn:string</code></a> function.</p></div></td></tr><tr class="xpath"><td style="vertical-align:top"><code>//author/@id</code></td><td style="vertical-align:top"><p>Supplying a sequence of nodes where a single string is expected will raise a type error unless either there is only one node in the sequence. In this case the typed value of the node will be used (this must be of type <code>xs:string</code>, <code>xs:untypedAtomic</code>, or <code>xs:anyURI</code>).</p><div class="xpath"><p class="xpath">If XPath 1.0 compatibility mode is enabled, however, all strings after the first are discarded, and the string value of the first node is used; if the sequence is empty, a zero-length string is supplied.</p></div></td></tr><tr class="xpath"><td style="vertical-align:top"><code>("red", "green", "blue")</code></td><td style="vertical-align:top"><p>Supplying a sequence of strings where a single string is expected raises a type error.</p><div class="xpath"><p class="xpath">If XPath 1.0 compatibility mode is enabled, however, all strings after the first are discarded; the effect is as if the supplied value were <code>"red"</code>.</p></div></td></tr><tr class="xpath"><td style="vertical-align:top"><code>()</code></td><td style="vertical-align:top"><p>Supplying an empty sequence where a single string is expected will fail.</p><div class="xpath"><p class="xpath">If XPath 1.0 compatibility mode is enabled, however, the value is coerced by applying the function <code>fn:string(())</code>, which delivers the zero-length string.</p></div></td></tr><tr><td style="vertical-align:top"><code>["a|b"]</code></td><td style="vertical-align:top"><p>Supplying an array holding a single string succeeds, because the rules cause the array to be atomized, and the value after atomization is a single string.</p><p>Supplying an array holding multiple strings would fail.</p><div class="xpath"><p class="xpath">In XPath 1.0 compatibility mode, supplying an array will fail, regardless of the array contents, because the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-string"><code>fn:string</code></a> function does not accept arrays.</p></div></td></tr></tbody></table></div></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-decimal"></a>Example: Coercion to <code>xs:decimal?</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:decimal?</code>. For example, the first argument of <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-seconds"><code>fn:seconds</code></a>, which expects a decimal number of seconds. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><div class="medium"><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>12.4</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>()</code></td><td style="vertical-align:top"><p>None; an empty sequence is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>42</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of <code>xs:integer</code>, which is a subtype of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>math:pi()</code></td><td style="vertical-align:top"><p>The supplied value is an instance of <code>xs:double</code>, which can be converted to <code>xs:decimal</code> under the coercion rules.</p></td></tr><tr><td style="vertical-align:top"><code>("a", "b")[.="c"]</code></td><td style="vertical-align:top"><p>The supplied value is an empty sequence, which is a valid instance of the required type <code>xs:decimal?</code>. However, the processor may (optionally) reject this as an implausible coercion, on the grounds that it can only succeed in one special case, namely where the filter expression selects no values. </p></td></tr><tr><td style="vertical-align:top"><code>(1.5, 2.5, 3.5)</code></td><td style="vertical-align:top"><p>A type error is raised<span class="xpath"><span class="xpath">, except in the case where XPath 1.0 compatibility is enabled, in which case all values after the first are discarded</span></span>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;3.14159&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The element node is atomized; unless it has been schema-validated, the result will be <code>"3.14159"</code> as an instance of <code>xs:untypedAtomic</code>. This is converted to an instance of <code>xs:decimal</code> following the rules of the <code>cast as</code> operator.</p></td></tr><tr class="xpath"><td style="vertical-align:top"><code>"12.2"</code></td><td style="vertical-align:top"><p>Supplying a string where an <code>xs:decimal</code> is a type error<span class="xpath"><span class="xpath">, even if XPath 1.0 compatibility mode is enabled. The rules for compatibility mode would allow conversion if the required type were <code>xs:double</code>, but not for <code>xs:decimal</code></span></span>. </p></td></tr><tr><td style="vertical-align:top"><code>[1.5]</code></td><td style="vertical-align:top"><p>The array is atomized, and the result is a valid instance of the required type <code>xs:decimal?</code></p></td></tr><tr><td style="vertical-align:top"><code>[]</code></td><td style="vertical-align:top"><p>The array is atomized, and the result is an empty sequence, which is a valid instance of the required type <code>xs:decimal?</code></p></td></tr></tbody></table></div></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-positive-integer"></a>Example: Coercion to <code>xs:positive-integer</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:positive-integer</code>. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><div class="medium"><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>12</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:integer</code>. Because the supplied value and the required type, <code>xs:positiveInteger</code>, both come under the primitive type <code>xs:decimal</code>, and the value <code>12</code> is within the value space of <code>xs:positiveInteger</code>, the value is relabeled as an <code>xs:positiveInteger</code> and the call succeeds.</p></td></tr><tr><td style="vertical-align:top"><code>12.1</code></td><td style="vertical-align:top"><p>This fails with a type error, because the <code>xs:decimal</code> value <code>12.1</code> is not a value in the value space of <code>xs:positiveInteger</code>. This is so even though casting to <code>xs:positiveInteger</code> would succeed.</p></td></tr><tr><td style="vertical-align:top"><code>math:pi()</code></td><td style="vertical-align:top"><p>This fails with a type error. A value of type <code>xs:double</code> is accepted where the required type is <code>xs:decimal</code> or <code>xs:float</code>, but not where it is <code>xs:positiveInteger</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;1200&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. If the element has not been schema-validated, the result will be an <code>xs:untypedAtomic</code> item, which is successfully cast to the required type <code>xs:positiveInteger</code>. If the element has been validated against a schema, then coercion succeeds if the typed value would itself be acceptable, for example if it is an <code>xs:positiveInteger</code>, or some other <code>xs:decimal</code> within the value space of <code>xs:positiveInteger</code>.</p></td></tr></tbody></table></div></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-union"></a>Example: Coercion to a union type</div><p>Consider the first parameter of the function <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a>, whose declared type is <code>(xs:string | xs:positiveInteger)</code>. The rules are the same as if it were a union typed declared in an imported schema.</p><div class="medium"><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>"amp"</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:string</code>, which is one of the allowed types. The call therefore succeeds.</p></td></tr><tr><td style="vertical-align:top"><code>"#"</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:string</code>, which is one of the allowed types. As far as the coercion rules are concerned, the call therefore succeeds. Under the semantic rules for the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a> function, however, this value is not accepted; a dynamic error (as distinct from a type error) is therefore raised.</p></td></tr><tr><td style="vertical-align:top"><code>0x25</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:integer</code>. Although this is not one of the allowed types, it is acceptable because coercion of the value to type <code>xs:positiveInteger</code> succeeds. The value is relabeled as an instance of <code>xs:positiveInteger</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;0x25&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. Assuming that the node has not been schema-validated, the result is an instance of <code>xs:untypedAtomic</code>. The member types of the choice are tested in order. Conversion to <code>xs:string</code> with the value "0x25" succeeds, so the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a> function is called supplying this string; but the function rejects this string as semantically invalid. The same would happen if the value were, say, &lt;a&gt;37&lt;/a&gt;. Supplying such a value requires an explicit cast, for example <code>fn:char( xs:positiveInteger( ./a ))</code>.</p></td></tr></tbody></table></div></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-choice"></a>Example: Coercion to a choice type</div><p>Suppose the required type is <code>(record(x as xs:decimal, y as xs:decimal, *) | record(size as enum("S", "M", "L", "XL"), *))</code>.</p><div class="medium"><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>{ "x": 1, "y": 2, "z": 3 }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of the first record type: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "size": "M" }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of the second record type: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1, "y": 2, "size": "XL" }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of both record types: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1e0, "y": 2e0, "size": "XL" }</code></td><td style="vertical-align:top"><p>The supplied value is not an instance of the first record type because the fields are of type <code>xs:double</code> rather than <code>xs:decimal</code>. It is however an instance of the second record type. It is therefore accepted <em>as is</em>; the fields <code>x</code> and <code>y</code> are not converted from <code>xs:double</code> to <code>xs:decimal</code>.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1e0, "y": 2e0, "size": "XXL" }</code></td><td style="vertical-align:top"><p>The supplied value is not an instance of the first record type because the fields are of type <code>xs:double</code> rather than <code>xs:decimal</code>, and it is not an instance of the second record type because the <code>size</code> value does not match the enumeration type. Coercion is therefore attempted to the first record type, and succeeds. The <code>x</code> and <code>y</code> fields are coerced to <code>xs:decimal</code>, and the <code>size</code> field is accepted <em>as is</em>.</p></td></tr></tbody></table></div></div></div></div><div class="div2"><h3><a id="id-predefined-types"></a>3.5 Schema Types</h3><p> [<a id="dt-schema-type" title="schema type">Definition</a>: A <b>schema type</b> is a complex type or simple type as defined in the <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> specifications, including built-in types as well as user-defined types.] </p><p>Every schema type is either a <b>complex type</b> or a <b>simple type</b>; simple types are further subdivided into <b>list types</b>, <b>union types</b>, and <b>atomic types</b> (see <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> for definitions and explanations of these terms.)</p><p>A schema type can appear as a type annotation on an element or attribute node. The type annotation on an element node can be a complex type or a simple type; the type annotation on an attribute node is always a simple type. Non-instantiable types such as <code>xs:NOTATION</code> or <code>xs:anyAtomicType</code> never appear as type annotations, but their derived types can be so used. Union types never appear as type annotations; when an element or attribute is validated against a union type, the resulting type annotation will be one of the types in the transitive membership of the union type.</p><p> [<a id="dt-atomic-type" title="atomic type">Definition</a>: An <b>atomic type</b> is a simple <a title="schema type" class="termref" href="#dt-schema-type">schema type</a> whose <a href="https://www.w3.org/TR/xmlschema11-1/#std-variety">{variety}<sup><small>XS11-1</small></sup></a> is <code>atomic</code>.] </p><p>An <b>atomic type</b> is either a built-in atomic type (defined either in the XSD specification or in this specification), or it is a user-defined atomic type included in an imported schema.</p><div class="xpath"><p class="xpath">The <a title="in-scope schema type" class="termref" href="#dt-is-types">in-scope schema types</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a> are initialized with a set of predefined schema types that is determined by the host language. This set may include some or all of the schema types in the namespace <code>http://www.w3.org/2001/XMLSchema</code>, represented in this document by the namespace prefix <code>xs</code>. The schema types in this namespace are defined in <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> and augmented by additional types defined in <a href="#xpath-datamodel-40">[XQuery and XPath Data Model (XDM) 4.0]</a>. An implementation that has based its type system on <a href="#XMLSchema10">[XML Schema 1.0]</a> is not required to support the <code>xs:dateTimeStamp</code> or <code>xs:error</code> types.</p></div><p>The schema types defined in <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#types-predefined">Section 2.8.3 Predefined Types</a><sup><small>DM</small></sup> are summarized below.</p><div class="xquery"><p class="xquery">The <a title="in-scope schema type" class="termref" href="#dt-is-types">in-scope schema types</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a> are initialized with certain predefined schema types, including the built-in schema types in the namespace <code>http://www.w3.org/2001/XMLSchema</code>, which has the predefined namespace prefix <code>xs</code>. The schema types in this namespace are defined in <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> and augmented by additional types defined in <a href="#xpath-datamodel-40">[XQuery and XPath Data Model (XDM) 4.0]</a>. Element and attribute declarations in the <code>xs</code> namespace are not implicitly included in the static context. The schema types defined in <a href="#xpath-datamodel-40">[XQuery and XPath Data Model (XDM) 4.0]</a> are summarized below.</p></div><ol class="enumar"><li><p> [<a id="dt-untyped" title="xs:untyped">Definition</a>: <code>xs:untyped</code> is used as the <a title="type annotation" class="termref" href="#dt-type-annotation">type annotation</a> of an element node that has not been validated, or has been validated in <code>skip</code> mode.] No predefined schema types are derived from <code>xs:untyped</code>.</p></li><li><p> [<a id="dt-untypedAtomic" title="xs:untypedAtomic">Definition</a>: <code>xs:untypedAtomic</code> is an <a title="atomic type" class="termref" href="#dt-atomic-type">atomic type</a> that is used to denote untyped atomic data, such as text that has not been assigned a more specific type.] An attribute that has been validated in <code>skip</code> mode is represented in the <a title="data model" class="termref" href="#dt-datamodel">data model</a> by an attribute node with the <a title="type annotation" class="termref" href="#dt-type-annotation">type annotation</a><code>xs:untypedAtomic</code>. No predefined schema types are derived from <code>xs:untypedAtomic</code>.</p></li><li><p> [<a id="dt-dayTimeDuration" title="xs:dayTimeDuration">Definition</a>: <code>xs:dayTimeDuration</code> is derived by restriction from <code>xs:duration</code>. The lexical representation of <code>xs:dayTimeDuration</code> is restricted to contain only day, hour, minute, and second components.] </p></li><li><p> [<a id="dt-yearMonthDuration" title="xs:yearMonthDuration">Definition</a>: <code>xs:yearMonthDuration</code> is derived by restriction from <code>xs:duration</code>. The lexical representation of <code>xs:yearMonthDuration</code> is restricted to contain only year and month components.] </p></li><li><p> [<a id="dt-anyAtomicType" title="xs:anyAtomicType">Definition</a>: <code>xs:anyAtomicType</code> is an <a title="atomic type" class="termref" href="#dt-atomic-type">atomic type</a> that includes all atomic items (and no values that are not atomic). Its base type is <code>xs:anySimpleType</code> from which all simple types, including atomic, list, and union types, are derived. All primitive atomic types, such as <code>xs:decimal</code> and <code>xs:string</code>, have <code>xs:anyAtomicType</code> as their base type.] </p><div class="note"><p class="prefix"><b>Note:</b></p><p><code>xs:anyAtomicType</code> will not appear as the type of an actual value in an <a title="XDM instance" class="termref" href="#dt-data-model-instance">XDM instance</a>.</p></div></li><li><p> [<a id="dt-xs-error" title="xs:error">Definition</a>: <code>xs:error</code> is a simple type with no value space. It is defined in <a href="https://www.w3.org/TR/xmlschema11-1/#xsd-error">Section 3.16.7.3 xs:error </a><sup><small>XS11-1</small></sup> and can be used in the <a href="#id-sequencetype-syntax"><b>3.1 Sequence Types</b></a> to raise errors.] </p></li></ol><p>The relationships among the schema types in the <code>xs</code> namespace are illustrated in Figure 2. A more complete description of the XQuery 4.0 and XPath 4.0 type hierarchy can be found in <a href="https://qt4cg.org/specifications/xpath-functions-40/#datatypes">Section 1.8 Type System</a><sup><small>FO</small></sup>.</p><img src="types.jpg" alt="Type Hierarchy Diagram"><p>Figure 2: Hierarchy of Schema Types used in XQuery 4.0 and XPath 4.0.</p></div></div><div class="div1"><h2><a id="id-expressions"></a>4 Expressions</h2><p>This section discusses each of the basic kinds of expression. Each kind of expression has a name such as <code>PathExpr</code>, which is introduced on the left side of the grammar production that defines the expression. Since XQuery 4.0 and XPath 4.0 is a composable language, each kind of expression is defined in terms of other expressions whose operators have a higher precedence. In this way, the precedence of operators is represented explicitly in the grammar.</p><p>The order in which expressions are discussed in this document does not reflect the order of operator precedence. In general, this document introduces the simplest kinds of expressions first, followed by more complex expressions. For the complete grammar, see Appendix [<a href="#nt-bnf"><b>A XQuery 4.0 and XPath 4.0 Grammar</b></a>].</p><p><span class="xpath"><span class="xpath">The highest-level symbol in the XPath grammar is XPath.</span></span><span class="xquery"><span class="xquery"> [<a id="dt-query" title="query">Definition</a>: A <b>query</b> consists of one or more <a title="module" class="termref" href="#dt-module">modules</a>.] If a query is executable, one of its modules has a <a title="query body" class="termref" href="#dt-queryBody">Query Body</a> containing an expression whose value is the result of the query. An expression is represented in the XQuery grammar by the symbol <a href="#doc-xpath40-Expr">Expr</a>.</span></span></p><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-XPath" id="doc-xpath40-XPath"></a>[1]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-XPath">XPath</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-Expr">Expr</a></code></td></tr><tr><td><code><a href="#doc-xpath40-Expr">Expr</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-Expr" id="doc-xpath40-Expr"></a>[46]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-Expr">Expr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>(<a href="#doc-xpath40-ExprSingle">ExprSingle</a> ++ ",")</code></td></tr><tr><td><code>(<a href="#doc-xpath40-ExprSingle">ExprSingle</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-ExprSingle" id="doc-xpath40-ExprSingle"></a>[47]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-ExprSingle">ExprSingle</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><span style="display: none;" class="delete_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xpath40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xpath40-OrExpr">OrExpr</a></code></span><span style="display: none;" class="add_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xpath40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xpath40-PipelineExpr">PipelineExpr</a></code></span><span class="modify_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xpath40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xpath40-OrExpr"><span class="deltaxml-old" style="background:#FF5555">OrExpr</span></a><a href="#doc-xpath40-PipelineExpr"><span class="deltaxml-new" style="background:#90EE90">PipelineExpr</span></a></code></span></td></tr><tr><td><span style="display: none;" class="delete_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xpath40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xpath40-OrExpr">OrExpr</a></code></span><span style="display: none;" class="add_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xpath40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xpath40-PipelineExpr">PipelineExpr</a></code></span><span class="modify_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xpath40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xpath40-OrExpr"><span class="deltaxml-old" style="background:#FF5555">OrExpr</span></a><a href="#doc-xpath40-PipelineExpr"><span class="deltaxml-new" style="background:#90EE90">PipelineExpr</span></a></code></span></td></tr></tbody></table><p>The XQuery 4.0 and XPath 4.0 operator that has lowest precedence is the <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a>, which is used to combine two operands to form a sequence. As shown in the grammar, a general expression (<a href="#doc-xpath40-Expr">Expr</a>) can consist of multiple <a href="#doc-xpath40-ExprSingle">ExprSingle</a> operands, separated by commas.</p><p>The name <a href="#doc-xpath40-ExprSingle">ExprSingle</a> denotes an expression that does not contain a top-level <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a> (despite its name, an <a href="#doc-xpath40-ExprSingle">ExprSingle</a> may evaluate to a sequence containing more than one item.)</p><p>The symbol <a href="#doc-xpath40-ExprSingle">ExprSingle</a> is used in various places in the grammar where an expression is not allowed to contain a top-level comma. For example, each of the arguments of a function call must be a <a href="#doc-xpath40-ExprSingle">ExprSingle</a>, because commas are used to separate the arguments of a function call.</p><p>After the comma, the expressions that have next lowest precedence are <span class="xquery"><span class="xquery"><a href="#doc-xpath40-FLWORExpr">FLWORExpr</a>,</span></span><span class="xpath"><span class="xpath"><a href="#doc-xpath40-ForExpr">ForExpr</a>, <a href="#doc-xpath40-LetExpr">LetExpr</a>, </span></span><a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a>, <span class="xquery"><span class="xquery"><a href="#doc-xpath40-SwitchExpr">SwitchExpr</a>, <a href="#doc-xpath40-TypeswitchExpr">TypeswitchExpr</a>, </span></span><a href="#doc-xpath40-IfExpr">IfExpr</a>, <span class="xquery"><span class="xquery"><a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a>, </span></span> and <a href="#doc-xpath40-OrExpr">OrExpr</a>. Each of these expressions is described in a separate section of this document.</p><div class="div2"><h3><a id="comments"></a>4.1 Comments</h3><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-Comment" id="doc-xpath40-Comment"></a>[<span class="deltaxml-old" style="background:#FF5555">282</span><span class="deltaxml-new" style="background:#90EE90">283</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-Comment">Comment</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"(:" (<a href="#doc-xpath40-CommentContents">CommentContents</a> | <a href="#doc-xpath40-Comment">Comment</a>)* ":)"</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>"(:" (<a href="#doc-xpath40-CommentContents">CommentContents</a> | <a href="#doc-xpath40-Comment">Comment</a>)* ":)"</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-comments">gn: comments</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-CommentContents" id="doc-xpath40-CommentContents"></a>[<span class="deltaxml-old" style="background:#FF5555">295</span><span class="deltaxml-new" style="background:#90EE90">296</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-CommentContents">CommentContents</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>(<a href="#prod-xpath40-Char">Char</a>+ - (Char* ('(:' | ':)') Char*))</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>(<a href="#prod-xpath40-Char">Char</a>+ - (Char* ('(:' | ':)') Char*))</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>Comments may be used to provide information relevant to programmers who read <span class="xquery"><span class="xquery">a query, either in the <a title="Prolog" class="termref" href="#dt-prolog">Prolog</a> or in the <a title="query body" class="termref" href="#dt-queryBody">Query Body</a></span></span><span class="xpath"><span class="xpath">an expression</span></span>. Comments are lexical constructs only, and do not affect <span class="xquery"><span class="xquery">query</span></span><span class="xpath"><span class="xpath">expression</span></span> processing.</p><p>Comments are strings, delimited by the symbols <code>(:</code> and <code>:)</code>. Comments may be nested.</p><p>A comment may be used anywhere <a title="ignorable whitespace" class="termref" href="#IgnorableWhitespace">ignorable whitespace</a> is allowed (see <a href="#DefaultWhitespaceHandling"><b>A.3.5.1 Default Whitespace Handling</b></a>).</p><p>The following is an example of a comment:</p><div class="exampleInner"><pre xml:space="preserve">(: Houston, we have a problem :)</pre></div></div><div class="div2"><h3><a id="id-primary-expressions"></a>4.2 Primary Expressions</h3><p> [<a id="dt-primary-expression" title="primary expression">Definition</a>: <b>Primary expressions</b> are the basic primitives of the language. They include literals, variable references, context value references, <span class="xquery"><span class="xquery">constructors, </span></span> and function calls. A primary expression may also be created by enclosing any expression in parentheses, which is sometimes helpful in controlling the precedence of operators.] <span class="xquery"><span class="xquery">Node Constructors are described in <a href="#id-constructors"><b>4.12 Node Constructors</b></a>.</span></span>Map and Array Constructors are described in <a href="#id-maps"><b>4.14.1 Maps</b></a> and <a href="#id-arrays"><b>4.14.2 Arrays</b></a>. <span class="xquery"><span class="xquery">String Constructors are described in <a href="#id-string-constructors"><b>4.9.3 String Constructors</b></a>.</span></span></p><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-PrimaryExpr" id="doc-xpath40-PrimaryExpr"></a>[<span class="deltaxml-old" style="background:#FF5555">170</span><span class="deltaxml-new" style="background:#90EE90">171</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-PrimaryExpr">PrimaryExpr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-Literal">Literal</a><br>| <a href="#doc-xpath40-VarRef">VarRef</a><br>| <a href="#doc-xpath40-ParenthesizedExpr">ParenthesizedExpr</a><br>| <a href="#doc-xpath40-ContextValueRef">ContextValueRef</a><br>| <a href="#doc-xpath40-FunctionCall">FunctionCall</a><br>| <a href="#doc-xpath40-OrderedExpr">OrderedExpr</a><br>| <a href="#doc-xpath40-UnorderedExpr">UnorderedExpr</a><br>| <a href="#doc-xpath40-NodeConstructor">NodeConstructor</a><br>| <a href="#doc-xpath40-FunctionItemExpr">FunctionItemExpr</a><br>| <a href="#doc-xpath40-MapConstructor">MapConstructor</a><br>| <a href="#doc-xpath40-ArrayConstructor">ArrayConstructor</a><br>| <a href="#doc-xpath40-StringTemplate">StringTemplate</a><br>| <a href="#doc-xpath40-StringConstructor">StringConstructor</a><br>| <a href="#doc-xpath40-UnaryLookup">UnaryLookup</a></code></td></tr><tr><td><code><a href="#doc-xpath40-Literal">Literal</a><br>| <a href="#doc-xpath40-VarRef">VarRef</a><br>| <a href="#doc-xpath40-ParenthesizedExpr">ParenthesizedExpr</a><br>| <a href="#doc-xpath40-ContextValueRef">ContextValueRef</a><br>| <a href="#doc-xpath40-FunctionCall">FunctionCall</a><br>| <a href="#doc-xpath40-OrderedExpr">OrderedExpr</a><br>| <a href="#doc-xpath40-UnorderedExpr">UnorderedExpr</a><br>| <a href="#doc-xpath40-NodeConstructor">NodeConstructor</a><br>| <a href="#doc-xpath40-FunctionItemExpr">FunctionItemExpr</a><br>| <a href="#doc-xpath40-MapConstructor">MapConstructor</a><br>| <a href="#doc-xpath40-ArrayConstructor">ArrayConstructor</a><br>| <a href="#doc-xpath40-StringTemplate">StringTemplate</a><br>| <a href="#doc-xpath40-StringConstructor">StringConstructor</a><br>| <a href="#doc-xpath40-UnaryLookup">UnaryLookup</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-FunctionItemExpr" id="doc-xpath40-FunctionItemExpr"></a>[<span class="deltaxml-old" style="background:#FF5555">209</span><span class="deltaxml-new" style="background:#90EE90">210</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-FunctionItemExpr">FunctionItemExpr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-NamedFunctionRef">NamedFunctionRef</a> | <a href="#doc-xpath40-InlineFunctionExpr">InlineFunctionExpr</a></code></td></tr><tr><td><code><a href="#doc-xpath40-NamedFunctionRef">NamedFunctionRef</a> | <a href="#doc-xpath40-InlineFunctionExpr">InlineFunctionExpr</a></code></td></tr></tbody></table><div class="div3"><h4><a id="id-literals"></a>4.2.1 Literals</h4><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-Literal" id="doc-xpath40-Literal"></a>[<span class="deltaxml-old" style="background:#FF5555">171</span><span class="deltaxml-new" style="background:#90EE90">172</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-Literal">Literal</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-NumericLiteral">NumericLiteral</a> | <a href="#doc-xpath40-StringLiteral">StringLiteral</a></code></td></tr><tr><td><code><a href="#doc-xpath40-NumericLiteral">NumericLiteral</a> | <a href="#doc-xpath40-StringLiteral">StringLiteral</a></code></td></tr></tbody></table><p> [<a id="dt-literal" title="literal">Definition</a>: A <b>literal</b> is a direct syntactic representation of an atomic item.] XQuery 4.0 and XPath 4.0 supports two kinds of literals: numeric literals and string literals.</p><div class="div4"><h5><a id="id-numeric-literals"></a>4.2.1.1 Numeric Literals</h5><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-filter-expression">⬇</a>&nbsp;<a href="#id-function-coercion">⬆</a></p><ol><li><p> Numeric literals can now be written in hexadecimal or binary notation; and underscores can be included for readability. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/429">429</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/433">433</a>&nbsp;25 April 2023]</i></p></li></ol></div><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-NumericLiteral" id="doc-xpath40-NumericLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">172</span><span class="deltaxml-new" style="background:#90EE90">173</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-NumericLiteral">NumericLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-IntegerLiteral">IntegerLiteral</a> | <a href="#doc-xpath40-HexIntegerLiteral">HexIntegerLiteral</a> | <a href="#doc-xpath40-BinaryIntegerLiteral">BinaryIntegerLiteral</a> | <a href="#doc-xpath40-DecimalLiteral">DecimalLiteral</a> | <a href="#doc-xpath40-DoubleLiteral">DoubleLiteral</a></code></td></tr><tr><td><code><a href="#doc-xpath40-IntegerLiteral">IntegerLiteral</a> | <a href="#doc-xpath40-HexIntegerLiteral">HexIntegerLiteral</a> | <a href="#doc-xpath40-BinaryIntegerLiteral">BinaryIntegerLiteral</a> | <a href="#doc-xpath40-DecimalLiteral">DecimalLiteral</a> | <a href="#doc-xpath40-DoubleLiteral">DoubleLiteral</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-IntegerLiteral" id="doc-xpath40-IntegerLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">266</span><span class="deltaxml-new" style="background:#90EE90">267</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-IntegerLiteral">IntegerLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-Digits">Digits</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code><a href="#doc-xpath40-Digits">Digits</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-HexIntegerLiteral" id="doc-xpath40-HexIntegerLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">267</span><span class="deltaxml-new" style="background:#90EE90">268</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-HexIntegerLiteral">HexIntegerLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"0x" <a href="#doc-xpath40-HexDigits">HexDigits</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>"0x" <a href="#doc-xpath40-HexDigits">HexDigits</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-BinaryIntegerLiteral" id="doc-xpath40-BinaryIntegerLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">268</span><span class="deltaxml-new" style="background:#90EE90">269</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-BinaryIntegerLiteral">BinaryIntegerLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"0b" <a href="#doc-xpath40-BinaryDigits">BinaryDigits</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>"0b" <a href="#doc-xpath40-BinaryDigits">BinaryDigits</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-DecimalLiteral" id="doc-xpath40-DecimalLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">269</span><span class="deltaxml-new" style="background:#90EE90">270</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-DecimalLiteral">DecimalLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>("." <a href="#doc-xpath40-Digits">Digits</a>) | (<a href="#doc-xpath40-Digits">Digits</a> "." <a href="#doc-xpath40-Digits">Digits</a>?)</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>("." <a href="#doc-xpath40-Digits">Digits</a>) | (<a href="#doc-xpath40-Digits">Digits</a> "." <a href="#doc-xpath40-Digits">Digits</a>?)</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-DoubleLiteral" id="doc-xpath40-DoubleLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">270</span><span class="deltaxml-new" style="background:#90EE90">271</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-DoubleLiteral">DoubleLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>(("." <a href="#doc-xpath40-Digits">Digits</a>) | (<a href="#doc-xpath40-Digits">Digits</a> ("." <a href="#doc-xpath40-Digits">Digits</a>?)?)) [eE] [+-]? <a href="#doc-xpath40-Digits">Digits</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>(("." <a href="#doc-xpath40-Digits">Digits</a>) | (<a href="#doc-xpath40-Digits">Digits</a> ("." <a href="#doc-xpath40-Digits">Digits</a>?)?)) [eE] [+-]? <a href="#doc-xpath40-Digits">Digits</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-Digits" id="doc-xpath40-Digits"></a>[<span class="deltaxml-old" style="background:#FF5555">289</span><span class="deltaxml-new" style="background:#90EE90">290</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-Digits">Digits</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-DecDigit">DecDigit</a> ((<a href="#doc-xpath40-DecDigit">DecDigit</a> | "_")* <a href="#doc-xpath40-DecDigit">DecDigit</a>)?</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code><a href="#doc-xpath40-DecDigit">DecDigit</a> ((<a href="#doc-xpath40-DecDigit">DecDigit</a> | "_")* <a href="#doc-xpath40-DecDigit">DecDigit</a>)?</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-DecDigit" id="doc-xpath40-DecDigit"></a>[<span class="deltaxml-old" style="background:#FF5555">290</span><span class="deltaxml-new" style="background:#90EE90">291</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-DecDigit">DecDigit</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>[0-9]</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>[0-9]</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-HexDigits" id="doc-xpath40-HexDigits"></a>[<span class="deltaxml-old" style="background:#FF5555">291</span><span class="deltaxml-new" style="background:#90EE90">292</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-HexDigits">HexDigits</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-HexDigit">HexDigit</a> ((<a href="#doc-xpath40-HexDigit">HexDigit</a> | "_")* <a href="#doc-xpath40-HexDigit">HexDigit</a>)?</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code><a href="#doc-xpath40-HexDigit">HexDigit</a> ((<a href="#doc-xpath40-HexDigit">HexDigit</a> | "_")* <a href="#doc-xpath40-HexDigit">HexDigit</a>)?</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-HexDigit" id="doc-xpath40-HexDigit"></a>[<span class="deltaxml-old" style="background:#FF5555">292</span><span class="deltaxml-new" style="background:#90EE90">293</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-HexDigit">HexDigit</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>[0-9a-fA-F]</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>[0-9a-fA-F]</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-BinaryDigits" id="doc-xpath40-BinaryDigits"></a>[<span class="deltaxml-old" style="background:#FF5555">293</span><span class="deltaxml-new" style="background:#90EE90">294</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-BinaryDigits">BinaryDigits</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-BinaryDigit">BinaryDigit</a> ((<a href="#doc-xpath40-BinaryDigit">BinaryDigit</a> | "_")* <a href="#doc-xpath40-BinaryDigit">BinaryDigit</a>)?</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code><a href="#doc-xpath40-BinaryDigit">BinaryDigit</a> ((<a href="#doc-xpath40-BinaryDigit">BinaryDigit</a> | "_")* <a href="#doc-xpath40-BinaryDigit">BinaryDigit</a>)?</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-BinaryDigit" id="doc-xpath40-BinaryDigit"></a>[<span class="deltaxml-old" style="background:#FF5555">294</span><span class="deltaxml-new" style="background:#90EE90">295</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-BinaryDigit">BinaryDigit</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>[01]</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>[01]</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>The value of a numeric literal is determined as follows (taking the rules in order):</p><ol class="enumar"><li><p>Underscore characters are stripped out. Underscores may be included in a numeric literal to aid readability, but have no effect on the value. For example, <code>1_000_000</code> is equivalent to <code>1000000</code>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Underscores must not appear at the beginning or end of a sequence of digits, only in intermediate positions. Multiple adjacent underscores are allowed.</p></div></li><li><p>A <code>HexIntegerLiteral</code> represents a non-negative integer expressed in hexadecimal: for example <code>0xffff</code> represents the integer 65535, and <code>0xFFFF_FFFF</code> represents the integer 4294967295.</p></li><li><p>A <code>BinaryIntegerLiteral</code> represents a non-negative integer expressed in binary: for example <code>0b101</code> represents the integer 5, and <code>0b1111_1111</code> represents the integer 255.</p></li><li><p>The value of a <b>numeric literal</b> containing no <code>.</code> and no <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:integer</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:integer</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li><li><p>The value of a numeric literal containing <code>.</code> but no <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:decimal</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:decimal</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li><li><p>The value of a numeric literal containing an <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:double</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:double</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li></ol><div class="note"><p class="prefix"><b>Note:</b></p><p>The value of a numeric literal is always non-negative. An expression may appear to include a negative number such as <code>-1</code>, but this is technically an arithmetic expression comprising a unary minus operator followed by a numeric literal.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The effect of the above rules is that in the case of an integer or decimal literal, a dynamic error [<a href="https://qt4cg.org/specifications/xpath-functions-40/#ERRFOAR0002" title="err:FOAR0002">err:FOAR0002</a>]<sup><small>FO40</small></sup> will generally be raised if the literal is outside the range of values supported by the implementation (other options are available: see <a href="https://qt4cg.org/specifications/xpath-functions-40/#op.numeric">Section 4.2 Arithmetic operators on numeric values</a><sup><small>FO</small></sup> for details.)</p><div class="xquery"><p class="xquery">The limits of numeric datatypes are specified in <a href="#id-data-model-conformance"><b>6.3 Data Model Conformance</b></a>.</p></div><div class="xpath"><p class="xpath">The XML Schema specification allows implementations to impose a limit (which must not be less than 18 digits) on the size of integer and decimal values. The full range of values of built-in subtypes of <code>xs:integer</code>, such as <code>xs:long</code> and <code>xs:unsignedLong</code>, can be supported only if the limit is 20 digits or higher. Negative numbers such as the minimum value of <code>xs:long</code> (<code>-9223372036854775808</code>) are technically unary expressions rather than literals, but implementations may prefer to ensure that they are expressible.</p></div></div><p>Here are some examples of numeric literals:</p><ul><li><p><code>12</code> denotes the <code>xs:integer</code> value twelve.</p></li><li><p><code>1_000_000</code> denotes the <code>xs:integer</code> value one million.</p></li><li><p><code>12.5</code> denotes the <code>xs:decimal</code> value twelve and one half.</p></li><li><p><code>3.14159_26535_89793e0</code> is an <code>xs:double</code> value representing the mathematical constant <var>π</var> to 15 decimal places. </p></li><li><p><code>125E2</code> denotes the <code>xs:double</code> value twelve thousand, five hundred.</p></li><li><p><code>0xffff</code> denotes the <code>xs:integer</code> value 65535.</p></li><li><p><code>0b1000_0001</code> denotes the <code>xs:integer</code> value 129.</p></li></ul></div><div class="div4"><h5><a id="id-string-literal"></a>4.2.1.2 String Literals</h5><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-StringLiteral" id="doc-xpath40-StringLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">271</span><span class="deltaxml-new" style="background:#90EE90">272</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-StringLiteral">StringLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-AposStringLiteral">AposStringLiteral</a> | <a href="#doc-xpath40-QuotStringLiteral">QuotStringLiteral</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code><a href="#doc-xpath40-AposStringLiteral">AposStringLiteral</a> | <a href="#doc-xpath40-QuotStringLiteral">QuotStringLiteral</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-AposStringLiteral" id="doc-xpath40-AposStringLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">272</span><span class="deltaxml-new" style="background:#90EE90">273</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-AposStringLiteral">AposStringLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"'" (<a href="#doc-xpath40-PredefinedEntityRef">PredefinedEntityRef</a> | <a href="#doc-xpath40-CharRef">CharRef</a> | <a href="#doc-xpath40-EscapeApos">EscapeApos</a> | [^'&amp;])* "'"</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>"'" (<a href="#doc-xpath40-PredefinedEntityRef">PredefinedEntityRef</a> | <a href="#doc-xpath40-CharRef">CharRef</a> | <a href="#doc-xpath40-EscapeApos">EscapeApos</a> | [^'&amp;])* "'"</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-QuotStringLiteral" id="doc-xpath40-QuotStringLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">273</span><span class="deltaxml-new" style="background:#90EE90">274</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-QuotStringLiteral">QuotStringLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>'"' (<a href="#doc-xpath40-PredefinedEntityRef">PredefinedEntityRef</a> | <a href="#doc-xpath40-CharRef">CharRef</a> | <a href="#doc-xpath40-EscapeQuot">EscapeQuot</a> | [^"&amp;])* '"'</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>'"' (<a href="#doc-xpath40-PredefinedEntityRef">PredefinedEntityRef</a> | <a href="#doc-xpath40-CharRef">CharRef</a> | <a href="#doc-xpath40-EscapeQuot">EscapeQuot</a> | [^"&amp;])* '"'</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-PredefinedEntityRef" id="doc-xpath40-PredefinedEntityRef"></a>[<span class="deltaxml-old" style="background:#FF5555">276</span><span class="deltaxml-new" style="background:#90EE90">277</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-PredefinedEntityRef">PredefinedEntityRef</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"&amp;" ("lt" | "gt" | "amp" | "quot" | "apos") ";"</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>"&amp;" ("lt" | "gt" | "amp" | "quot" | "apos") ";"</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-CharRef" id="doc-xpath40-CharRef"></a>[<span class="deltaxml-old" style="background:#FF5555">284</span><span class="deltaxml-new" style="background:#90EE90">285</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-CharRef">CharRef</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="https://www.w3.org/TR/REC-xml/#NT-CharRef">[http://www.w3.org/TR/REC-xml#NT-CharRef]</a><sup><small>XML</small></sup></code></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-xml-version">xgc: xml-version</a> */</td></tr><tr><td><code><a href="https://www.w3.org/TR/REC-xml/#NT-CharRef">[http://www.w3.org/TR/REC-xml#NT-CharRef]</a><sup><small>XML</small></sup></code></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-xml-version">xgc: xml-version</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-xml-version">xgc: xml-version</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-EscapeQuot" id="doc-xpath40-EscapeQuot"></a>[<span class="deltaxml-old" style="background:#FF5555">277</span><span class="deltaxml-new" style="background:#90EE90">278</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-EscapeQuot">EscapeQuot</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>'""'</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>'""'</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-EscapeApos" id="doc-xpath40-EscapeApos"></a>[<span class="deltaxml-old" style="background:#FF5555">278</span><span class="deltaxml-new" style="background:#90EE90">279</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-EscapeApos">EscapeApos</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"''"</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>"''"</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>The value of a <b>string literal</b> is an atomic item whose type is <code>xs:string</code> and whose value is the string denoted by the characters between the delimiting apostrophes or quotation marks. If the literal is delimited by apostrophes, two adjacent apostrophes within the literal are interpreted as a single apostrophe. Similarly, if the literal is delimited by quotation marks, two adjacent quotation marks within the literal are interpreted as one quotation mark.</p><div class="xquery"><p class="xquery"> [<a id="dt-predefined-entity-reference" title="predefined entity reference">Definition</a>: A <b>predefined entity reference</b> is a short sequence of characters, beginning with an ampersand, that represents a single character that might otherwise have syntactic significance.] Each predefined entity reference is replaced by the character it represents when the string literal is processed. The predefined entity references recognized by XPath and XQuery are as follows:</p></div><div class="xquery"><div class="medium"><table style="width:60%; border:1px solid" class="medium"><tbody><tr><th style="text-align:center">Entity Reference</th><th style="text-align:center">Character Represented</th></tr><tr><td style="text-align:center"><code>&amp;lt;</code></td><td style="text-align:center"><code>&lt;</code></td></tr><tr><td style="text-align:center"><code>&amp;gt;</code></td><td style="text-align:center"><code>&gt;</code></td></tr><tr><td style="text-align:center"><code>&amp;amp;</code></td><td style="text-align:center"><code>&amp;</code></td></tr><tr><td style="text-align:center"><code>&amp;quot;</code></td><td style="text-align:center"><code>"</code></td></tr><tr><td style="text-align:center"><code>&amp;apos;</code></td><td style="text-align:center"><code>'</code></td></tr></tbody></table></div></div><div class="xquery"><p class="xquery"> [<a id="dt-character-reference" title="character reference">Definition</a>: A <b>character reference</b> is an XML-style reference to a <a href="#Unicode">[Unicode]</a> character, identified by its decimal or hexadecimal codepoint.] For example, the character <span class="unicode-codepoint">U+20AC</span> (<span class="unicode-name">EURO SIGN</span>, <code>€</code>) can be represented by the character reference <code>&amp;#8364;</code> or <code>&amp;#x20ac;</code>. Character references are normatively defined in Section 4.1 of the XML specification (it is <a title="implementation defined" class="termref" href="#dt-implementation-defined">implementation-defined</a> whether the rules in <a href="#XML">[XML 1.0]</a> or <a href="#XML1.1">[XML 1.1]</a> apply.) A <a title="static error" class="termref" href="#dt-static-error">static error</a> [<a href="#ERRXQST0090" title="err:XQST0090">err:XQST0090</a>] is raised if a character reference does not identify a valid character in the version of XML that is in use.</p></div><p>Here are some examples of string literals:</p><ul><li><p><code>"He said, ""I don't like it."""</code> denotes a string containing two quotation marks and one apostrophe.</p></li><li class="xquery"><p><code>"Ben &amp;amp; Jerry&amp;apos;s"</code> denotes the <code>xs:string</code> value <code>"Ben &amp; Jerry's"</code>.</p></li><li class="xquery"><p><code>"&amp;#8364;99.50"</code> denotes the <code>xs:string</code> value <code>"€99.50"</code>.</p></li><li><p>In XQuery, the string literal <code>"&amp;lt;"</code> denotes a string of length 1 containing the single character <code>"&lt;"</code>. In XPath, the string literal <code>"&amp;lt;"</code> denotes a string of length 4 containing the four characters <code>"&amp;"</code>, <code>"l"</code>, <code>"t"</code>, <code>";"</code>. (However, when the XPath expression is embedded in an XML document, the sequence <code>"&amp;lt;"</code> will typically have already been converted to <code>"&lt;"</code> by the XML parser.)</p></li></ul><div class="note"><p class="prefix"><b>Note:</b></p><p>When XPath or XQuery expressions are embedded in contexts where quotation marks have special significance, such as inside XML attributes, or in string literals in a host language such as Java or C#, then additional escaping may be needed.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>Fixed string values can also be written as string templates: see <a href="#id-string-templates"><b>4.9.2 String Templates</b></a>. A string template with no enclosed expressions, such as <code>`Jamaica`</code> evaluates to the same value as the string literals <code>"Jamaica"</code> or <code>'Jamaica'</code>. A string template can contain both single and double quotation marks: <code>`He said: "I don't like it"`</code>. However, there there are some subtle differences:</p><ul><li><p>In string literals, the treatment of character and entity references such as <code>&amp;amp;</code> varies between XQuery and XPath; in string templates, such references are not expanded in either language.</p></li><li><p>String templates can only be used where an expression is expected. String literals are also used in some non-expression contexts, for example in defining an enumeration type: see <a href="#id-enumeration-types"><b>3.2.6 Enumeration Types</b></a>.</p></li><li><p>Curly brackets (<span class="unicode-codepoint">U+007B</span> (<span class="unicode-name">LEFT CURLY BRACKET</span>, <code>{</code>) and <span class="unicode-codepoint">U+007D</span> (<span class="unicode-name">RIGHT CURLY BRACKET</span>, <code>}</code>) ) and backticks (<span class="unicode-codepoint">U+0060</span> (<span class="unicode-name">GRAVE ACCENT, BACKTICK</span>, <code>`</code>) ) have a reserved meaning in string templates.</p></li></ul></div></div><div class="div4"><h5><a id="id-constants-other-types"></a>4.2.1.3 Constants of Other Types</h5><p> The <code>xs:boolean</code> values <code>true</code> and <code>false</code> can be constructed by calls to the <a title="system function" class="termref" href="#dt-system-function">system functions</a><code>fn:true()</code> and <code>fn:false()</code>, respectively. </p><p>Values of other simple types can be constructed by calling the <a title="constructor function" class="termref" href="#dt-constructor-function">constructor function</a> for the given type. The constructor functions for XML Schema built-in types are defined in <a href="https://qt4cg.org/specifications/xpath-functions-40/#constructor-functions-for-xsd-types">Section 20.1 Constructor functions for XML Schema built-in atomic types</a><sup><small>FO</small></sup>. In general, the name of a constructor function for a given type is the same as the name of the type (including its namespace). For example:</p><ul><li><p><code>xs:integer("12")</code> returns the integer value twelve.</p></li><li><p><code>xs:date("2001-08-25")</code> returns an item whose type is <code>xs:date</code> and whose value represents the date 25th August 2001.</p></li><li><p><code>xs:dayTimeDuration("PT5H")</code> returns an item whose type is <code>xs:dayTimeDuration</code> and whose value represents a duration of five hours.</p></li></ul><p>Constructor functions can also be used to create special values that have no literal representation, as in the following examples: </p><ul><li><p><code>xs:float("NaN")</code> returns the special floating-point value, "Not a Number."</p></li><li><p><code>xs:double("INF")</code> returns the special double-precision value, "positive infinity."</p></li></ul><p>Constructor functions are available for all simple types, including union types. For example, if <code>my:dt</code> is a user-defined union type whose member types are <code>xs:date</code>, <code>xs:time</code>, and <code>xs:dateTime</code>, then the expression <code>my:dt("2011-01-10")</code> creates an atomic item of type <code>xs:date</code>. The rules follow XML Schema validation rules for union types: the effect is to choose the first member type that accepts the given string in its lexical space.</p><p>It is also possible to construct values of various types by using a <code>cast</code> expression. For example:</p><ul><li><p><code>9 cast as hatsize</code> returns the atomic item <code>9</code> whose type is <code>hatsize</code>.</p></li></ul></div></div><div class="div3"><h4><a id="id-variables"></a>4.2.2 Variable References</h4><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-VarRef" id="doc-xpath40-VarRef"></a>[<span class="deltaxml-old" style="background:#FF5555">173</span><span class="deltaxml-new" style="background:#90EE90">174</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-VarRef">VarRef</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"$" <a href="#doc-xpath40-EQName">EQName</a></code></td></tr><tr><td><code>"$" <a href="#doc-xpath40-EQName">EQName</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="noid_d4e15028.doc-xpath40-EQName" id="noid_d4e15028.doc-xpath40-EQName"></a>[<span class="deltaxml-old" style="background:#FF5555">265</span><span class="deltaxml-new" style="background:#90EE90">266</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-EQName">EQName</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-QName">QName</a> | <a href="#doc-xpath40-URIQualifiedName">URIQualifiedName</a></code></td></tr><tr><td><code><a href="#doc-xpath40-QName">QName</a> | <a href="#doc-xpath40-URIQualifiedName">URIQualifiedName</a></code></td></tr></tbody></table><p> [<a id="dt-variable-reference" title="variable reference">Definition</a>: A <b>variable reference</b> is an EQName preceded by a $-sign.] An unprefixed variable reference is in no namespace. Two variable references are equivalent if their <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QNames</a> are equal (as defined by the <code>eq</code> operator). The scope of a variable binding is defined separately for each kind of expression that can bind variables.</p><p>Every variable reference must match a name in the <a title="in-scope variables" class="termref" href="#dt-in-scope-variables">in-scope variables</a>. </p><p>Every variable binding has a static scope. The scope defines where references to the variable can validly occur. It is a <a title="static error" class="termref" href="#dt-static-error">static error</a> [<a href="#ERRXPST0008" title="err:XPST0008">err:XPST0008</a>] to reference a variable that is not in scope. If a variable is bound in the <a title="static context" class="termref" href="#dt-static-context">static context</a> for an expression, that variable is in scope for the entire expression except where it is occluded by another binding that uses the same name within that scope.</p><div class="xquery"><p class="xquery">A reference to a variable that was declared <code>external</code>, but was not bound to a value by the external environment, raises a <a title="dynamic error" class="termref" href="#dt-dynamic-error">dynamic error</a> [<a href="#ERRXPDY0002" title="err:XPDY0002">err:XPDY0002</a>].</p></div><p> At evaluation time, the value of a variable reference is the value to which the relevant variable is bound.</p></div><div class="div3"><h4><a id="id-context-value-references"></a>4.2.3 Context Value References</h4><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-ContextValueRef" id="doc-xpath40-ContextValueRef"></a>[<span class="deltaxml-old" style="background:#FF5555">175</span><span class="deltaxml-new" style="background:#90EE90">176</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-ContextValueRef">ContextValueRef</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"."</code></td></tr><tr><td><code>"."</code></td></tr></tbody></table><p>A <b>context value reference</b> evaluates to the <a title="context value" class="termref" href="#dt-context-value">context value</a>.</p><p>In many syntactic contexts, the context value will be a single item. For example this applies on the right-hand side of the <code>/</code> or <code>!</code> operators, or within a <a href="#doc-xpath40-Predicate">Predicate</a>.</p><p>If the <a title="context value" class="termref" href="#dt-context-value">context value</a> is <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#dt-absent">absent</a><sup><small>DM</small></sup>, a context value reference raises a <a title="type error" class="termref" href="#dt-type-error">type error</a> [<a href="#ERRXPDY0002" title="err:XPDY0002">err:XPDY0002</a>].</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Being absent is not the same thing as being empty.</p></div></div><div class="div3"><h4><a id="id-paren-expressions"></a>4.2.4 Parenthesized Expressions</h4><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-ParenthesizedExpr" id="doc-xpath40-ParenthesizedExpr"></a>[<span class="deltaxml-old" style="background:#FF5555">174</span><span class="deltaxml-new" style="background:#90EE90">175</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-ParenthesizedExpr">ParenthesizedExpr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"(" <a href="#doc-xpath40-Expr">Expr</a>? ")"</code></td></tr><tr><td><code>"(" <a href="#doc-xpath40-Expr">Expr</a>? ")"</code></td></tr></tbody></table><p>Parentheses may be used to override the precedence rules. For example, the expression <code>(2 + 4) * 5</code> evaluates to thirty, since the parenthesized expression <code>(2 + 4)</code> is evaluated first and its result is multiplied by five. Without parentheses, the expression <code>2 + 4 * 5</code> evaluates to twenty-two, because the multiplication operator has higher precedence than the addition operator.</p><p>Empty parentheses are used to denote an empty sequence, as described in <a href="#construct_seq"><b>4.7.1 Sequence Concatenation</b></a>.</p></div><div class="div3"><h4><a id="id-enclosed-expr"></a>4.2.5 Enclosed Expressions</h4><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-EnclosedExpr" id="doc-xpath40-EnclosedExpr"></a>[40]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-EnclosedExpr">EnclosedExpr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"{" <a href="#doc-xpath40-Expr">Expr</a>? "}"</code></td></tr><tr><td><code>"{" <a href="#doc-xpath40-Expr">Expr</a>? "}"</code></td></tr></tbody></table><p> [<a id="dt-enclosed-expression" title="enclosed expression">Definition</a>: An <b>enclosed expression</b> is an instance of the <a href="#doc-xpath40-EnclosedExpr">EnclosedExpr</a> production, which allows an optional expression within curly brackets.] [<a id="dt-content-expression" title="content expression">Definition</a>: In an <a title="enclosed expression" class="termref" href="#dt-enclosed-expression">enclosed expression</a>, the optional expression enclosed in curly brackets is called the <b>content expression</b>.] If the <a title="content expression" class="termref" href="#dt-content-expression">content expression</a> is not provided explicitly, the content expression is <code>()</code>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Despite the name, an enclosed expression is not actually an expression in its own right; rather it is a construct that is used in the grammar of many other expressions.</p></div></div></div><div class="div2"><h3><a id="id-postfix-expression"></a>4.3 Postfix Expressions</h3><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-PostfixExpr" id="doc-xpath40-PostfixExpr"></a>[<span class="deltaxml-old" style="background:#FF5555">154</span><span class="deltaxml-new" style="background:#90EE90">155</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-PostfixExpr">PostfixExpr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-PrimaryExpr">PrimaryExpr</a> | <a href="#doc-xpath40-FilterExpr">FilterExpr</a> | <a href="#doc-xpath40-DynamicFunctionCall">DynamicFunctionCall</a> | <a href="#doc-xpath40-LookupExpr">LookupExpr</a> | <a href="#doc-xpath40-FilterExprAM">FilterExprAM</a></code></td></tr><tr><td><code><a href="#doc-xpath40-PrimaryExpr">PrimaryExpr</a> | <a href="#doc-xpath40-FilterExpr">FilterExpr</a> | <a href="#doc-xpath40-DynamicFunctionCall">DynamicFunctionCall</a> | <a href="#doc-xpath40-LookupExpr">LookupExpr</a> | <a href="#doc-xpath40-FilterExprAM">FilterExprAM</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="noid_d4e15160.doc-xpath40-FilterExpr" id="noid_d4e15160.doc-xpath40-FilterExpr"></a>[<span class="deltaxml-old" style="background:#FF5555">153</span><span class="deltaxml-new" style="background:#90EE90">154</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-FilterExpr">FilterExpr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Predicate">Predicate</a></code></td></tr><tr><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Predicate">Predicate</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="noid_d4e15161.doc-xpath40-DynamicFunctionCall" id="noid_d4e15161.doc-xpath40-DynamicFunctionCall"></a>[<span class="deltaxml-old" style="background:#FF5555">155</span><span class="deltaxml-new" style="background:#90EE90">156</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-DynamicFunctionCall">DynamicFunctionCall</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-PositionalArgumentList">PositionalArgumentList</a></code></td></tr><tr><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-PositionalArgumentList">PositionalArgumentList</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="noid_d4e15162.doc-xpath40-LookupExpr" id="noid_d4e15162.doc-xpath40-LookupExpr"></a>[<span class="deltaxml-old" style="background:#FF5555">162</span><span class="deltaxml-new" style="background:#90EE90">163</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-LookupExpr">LookupExpr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Lookup">Lookup</a></code></td></tr><tr><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Lookup">Lookup</a></code></td></tr></tbody></table><p>A postfix expression takes one of the following forms:</p><ul><li><p> [<a id="dt-filter-expression" title="filter expression">Definition</a>: A <b>filter expression</b> is an expression in the form <code>E1[E2]</code>: its effect is to return those items from the value of <code>E1</code> that satisfy the predicate in E2.] </p><p>Filter expressions are described in <a href="#id-filter-expression"><b>4.4 Filter Expressions</b></a>.</p><p>An example of a filter expression is <code>(1 to 100)[. mod 2 = 0]</code> which returns all even numbers in the range 1 to 100.</p><p>The base expression <code>E1</code> can itself be a postfix expression, so multiple predicates are allowed, in the form <code>E1[E2][E3][E4]</code>.</p></li><li><p>An expression (other than a raw EQName) followed by an argument list in parentheses (that is, <code>E1(E2, E3, ...)</code>) is referred to as a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-invocation">dynamic function call</a>. Its effect is to evaluate <code>E1</code> to obtain a function, and then call that function, with <code>E2</code>, <code>E3</code>, <code>...</code> as arguments. Dynamic function calls are described in <a href="#id-dynamic-function-invocation"><b>4.5.2.1 Dynamic Function Calls</b></a>.</p><p>An example of a dynamic function call is <code>$f("a", 2)</code> where the value of variable <code>$f</code> must be a function item.</p></li><li><p>A <code>lookup-expression</code> takes the form <code>E1?K</code>, where <code>E1</code> is an expression returning a sequence of maps or arrays, and <code>K</code> is a key specifier, which indicates which entries in a map, or members in an array, should be selected.</p><p>Lookup expressions are described in <a href="#id-postfix-lookup"><b>4.14.3.1 Postfix Lookup Expressions</b></a>.</p><p>An example of a lookup expression is <code>$emp?name</code>, where the value of variable <code>$emp</code> is a map, and the string <code>"name"</code> is the key of one of the entries in the map.</p></li></ul><p>Postfix expressions are evaluated from left-to-right. For example, the expression <code>$E1[E2]?(E3)(E4)</code> is evaluated by first evaluating the filter expression <code>$E1[E2]</code> to produce a sequence of maps and arrays (say <code>$S</code>), then evaluating the lookup expression <code>$S?(E3)</code> to produce a function item (say <code>$F</code>), then evaluating the dynamic function call <code>$F(E4)</code> to produce the final result.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>The grammar for postfix expressions is defined here in a way designed to link clearly to the semantics of the different kinds of expression. For parsing purposes, the equivalent production rule:</p><div class="exampleInner"><pre xml:space="preserve">PostfixExpr := PrimaryExpr (Predicate | PositionalArgumentList | Lookup)*</pre></div><p>(as used in XPath 3.1) is probably more convenient.</p></div></div><div class="div2"><h3><a id="id-filter-expression"></a>4.4 Filter Expressions</h3><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-function-calls">⬇</a>&nbsp;<a href="#id-numeric-literals">⬆</a></p><ol><li><p> The value of a predicate in a filter expression can now be a sequence of integers. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/816">816</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/996">996</a>&nbsp;6 February 2024]</i></p></li></ol></div><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-FilterExpr" id="doc-xpath40-FilterExpr"></a>[<span class="deltaxml-old" style="background:#FF5555">153</span><span class="deltaxml-new" style="background:#90EE90">154</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-FilterExpr">FilterExpr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Predicate">Predicate</a></code></td></tr><tr><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Predicate">Predicate</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-Predicate" id="doc-xpath40-Predicate"></a>[<span class="deltaxml-old" style="background:#FF5555">161</span><span class="deltaxml-new" style="background:#90EE90">162</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-Predicate">Predicate</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"[" <a href="#doc-xpath40-Expr">Expr</a> "]"</code></td></tr><tr><td><code>"[" <a href="#doc-xpath40-Expr">Expr</a> "]"</code></td></tr></tbody></table><p>A filter expression consists of a base expression followed by a predicate, which is an expression written in square brackets. The result of the filter expression consists of the items returned by the base expression, filtered by applying the predicate to each item in turn. The ordering of the items returned by a filter expression is the same as their order in the result of the primary expression.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Where the expression before the square brackets is a <a href="#doc-xpath40-ReverseStep">ReverseStep</a> or <a href="#doc-xpath40-ForwardStep">ForwardStep</a>, the expression is technically not a filter expression but an <a href="#doc-xpath40-AxisStep">AxisStep</a>. There are minor differences in the semantics: see <a href="#id-predicate"><b>4.6.5 Predicates within Steps</b></a></p></div><p>Here are some examples of filter expressions:</p><ul><li><p>Given a sequence of products in a variable, return only those products whose price is greater than 100.</p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">$products[price gt 100]</pre></div></div></li><li><p>List all the integers from 1 to 100 that are divisible by 5. (See <a href="#construct_seq"><b>4.7.1 Sequence Concatenation</b></a> for an explanation of the <code>to</code> operator.)</p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">(1 to 100)[. mod 5 eq 0]</pre></div></div></li><li><p>The result of the following expression is the integer 25:</p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">(21 to 29)[5]</pre></div></div></li><li><p>The following example returns the fifth through ninth items in the sequence bound to variable <code>$orders</code>.</p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">$orders[5 to 9]</pre></div></div></li><li><p>The following example illustrates the use of a filter expression as a <a title="step" class="termref" href="#dt-step">step</a> in a <a title="path expression" class="termref" href="#dt-path-expression">path expression</a>. It returns the last chapter or appendix within the book bound to variable <code>$book</code>:</p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">$book/(chapter | appendix)[last()]</pre></div></div></li></ul><p>For each item in the input sequence, the predicate expression is evaluated using an <b>inner focus</b>, defined as follows: The context value is the item currently being tested against the predicate. The context size is the number of items in the input sequence. The context position is the position of the context value within the input sequence. </p><p>For each item in the input sequence, the result of the predicate expression is coerced to an <code>xs:boolean</code> value, called the <a title="predicate truth value" class="termref" href="#dt-predicate-truth-value">predicate truth value</a>, as described below. Those items for which the predicate truth value is <code>true</code> are retained, and those for which the predicate truth value is <code>false</code> are discarded.</p><p> [<a id="dt-predicate-truth-value" title="predicate truth value">Definition</a>: The <b>predicate truth value</b> of a value <code>$V</code> is the result of the expression <code>if ($V instance of xs:numeric+) then ($V = position()) else fn:boolean($V)</code>.] </p><p>Expanding this definition, the predicate truth value can be obtained by applying the following rules, in order:</p><ol class="enumar"><li><p>If the value <var>V</var> of the predicate expression is a sequence whose first item is an instance of the type <code>xs:numeric</code>, then:</p><ol class="enumla"><li><p><var>V</var> must be an instance of the type <code>xs:numeric+</code> (that is, every item in <var>V</var> must be numeric). A type error [<a href="https://qt4cg.org/specifications/xpath-functions-40/#ERRFORG0006" title="err:FORG0006">err:FORG0006</a>]<sup><small>FO40</small></sup> is raised if this is not the case.</p></li><li><p>The predicate truth value is <code>true</code> if <var>V</var> is equal (by the <code>=</code> operator) to the <b>context position</b>, and is <code>false</code> otherwise.</p></li></ol><p>In effect this means that an item in the input sequence is selected if its position in the sequence is equal to one or more of the numeric values in the predicate. For example, the predicate <code>[3 to 5]</code> is true for the third, fourth, and fifth items in the input sequence.</p><p><span class="xquery">[<a id="dt-numeric-predicate" title="numeric predicate">Definition</a>: A predicate whose predicate expression returns a value of type <code>xs:numeric+</code> is called a <b>numeric predicate</b>.]</span></p><div class="note"><p class="prefix"><b>Note:</b></p><p>It is possible, though not generally useful, for the value of a numeric predicate to depend on the focus, and thus to differ for different items in the input sequence. For example, the predicate <code>[xs:integer(@seq)]</code> selects those items in the input sequence whose <code>@seq</code> attribute is numerically equal to their position in the input sequence.</p><p>It is also possible, and again not generally useful, for the value of the predicate to be numeric for some items in the input sequence, and boolean for others. For example, the predicate <code>[@special otherwise last()]</code> is true for an item that either has an <code>@special</code> attribute, or is the last item in the input sequence.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The truth value of a numeric predicate does not depend on the order of the numbers in <var>V</var>. The predicates <code>[ 1, 2, 3 ]</code> and <code>[ 3, 2, 1 ]</code> have exactly the same effect. The items in the result of a filter expression always retain the ordering of the input sequence.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The truth value of a numeric predicate whose value is non-integral or non-positive is always false.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>Beware that using boolean operators (<code>and</code>, <code>or</code>, <code>not()</code>) with numeric values may not have the intended effect. For example the predicate <code>[1 or last()]</code> selects every item in the sequence, because <code>or</code> operates on the <a title="effective boolean value" class="termref" href="#dt-ebv">effective boolean value</a> of its operands. The required effect can be achieved with the predicate <code>[1, last()]</code>.</p></div></li><li><p>Otherwise, the predicate truth value is the <a title="effective boolean value" class="termref" href="#dt-ebv">effective boolean value</a> of the predicate expression.</p></li></ol></div><div class="div2"><h3><a id="id-functions"></a>4.5 Functions</h3><p>Functions in XQuery 4.0 and XPath 4.0 arise in two ways:</p><ul><li><p>A <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> contains information about a family of functions with the same name and a defined arity range. These functions are in most cases known statically (they appear in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a>), but there may be further function definitions that are known only dynamically (appearing in the <a title="dynamically known function definitions" class="termref" href="#dt-dynamically-known-function-definitions">dynamically known function definitions</a>).</p></li><li><p><a title="function item" class="termref" href="#dt-function-item">Function items</a> are XDM items that can be called using a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-call">dynamic function call</a>. They are values that can be bound to variables, passed as arguments, returned as function results, and generally manipulated in the same way as other XDM values.</p></li></ul><p>The functions defined by a statically known <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> can be invoked using a <a title="static function call" class="termref" href="#dt-static-function-call">static function call</a>. <a title="function item" class="termref" href="#dt-function-item">Function items</a> corresponding to these definitions can also be obtained, as dynamic values, by evaluating a <a title="named function reference" class="termref" href="#dt-named-function-ref">named function reference</a>. <a title="function item" class="termref" href="#dt-function-item">Function items</a> can also be obtained using the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-function-lookup"><code>fn:function-lookup</code></a> function: in this case the function name and arity do not need to be known statically, and the function definition need not be present in the <a title="static context" class="termref" href="#dt-static-context">static context</a>, so long as it is in the <a title="dynamic context" class="termref" href="#dt-dynamic-context">dynamic context</a>.</p><p>Static and dynamic function calls are described in the following sections.</p><div class="div3"><h4><a id="id-static-functions"></a>4.5.1 Static Function Calls</h4><p>The <a title="static context" class="termref" href="#dt-static-context">static context</a> for an expression includes a set of <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a>. Every <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context has a name (which is an <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a>) and an <a title="arity range" class="termref" href="#dt-arity-range">arity range</a>, which is a range of permitted arities for calls on that function. Two <a title="function definition" class="termref" href="#dt-function-definition">function definitions</a> having the same name must not have overlapping arity ranges. This means that for a given static function call, it is possible to identify the target function definition in the static context unambiguously from knowledge of the function name and the number of supplied arguments.</p><p>A <a title="static function call" class="termref" href="#dt-static-function-call">static function call</a> is bound to a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context by matching the name and arity. If the function call has <var>P</var> positional arguments followed by <var>K</var> keyword arguments, then the required arity is <var>P+K</var>, and the static context must include a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> whose name matches the <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a> in the function call, and whose <a title="arity range" class="termref" href="#dt-arity-range">arity range</a> includes this required arity. This is the function chosen to be called. The result of the function is obtained by evaluating the expression that forms its implementation, with a dynamic context that provides values for all the declared parameters, initialized as described in <a href="#id-eval-static-function-call"><b>4.5.1.2 Evaluating Static Function Calls</b></a> below.</p><p>Similarly, a function reference of the form <code>f#N</code> binds to a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context whose name matches <var>f</var> where <code>MinP ≤ N and MaxP ≥ N</code>. The result of evaluating a function reference is a <a title="function item" class="termref" href="#dt-function-item">function item</a> which can be called using a dynamic function call. Function items are never variadic and their arguments are always supplied positionally. For example, the function reference <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-concat"><code>fn:concat#3</code></a> returns a function item with arity 3, which is always called by supplying three positional arguments, and whose effect is the same as a static call on <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-concat"><code>fn:concat</code></a> with three positional arguments. </p><p>The detailed rules for evaluating static function calls and function references are defined in subsequent sections.</p><div class="div4"><h5><a id="id-function-calls"></a>4.5.1.1 Static Function Call Syntax</h5><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-inline-func">⬇</a>&nbsp;<a href="#id-filter-expression">⬆</a></p><ol><li><p> Keyword arguments are allowed on static function calls, as well as positional arguments. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/155">155</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/159">159</a>&nbsp;30 September 2020]</i></p></li></ol></div><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-FunctionCall" id="doc-xpath40-FunctionCall"></a>[<span class="deltaxml-old" style="background:#FF5555">178</span><span class="deltaxml-new" style="background:#90EE90">179</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-FunctionCall">FunctionCall</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-EQName">EQName</a><a href="#doc-xpath40-ArgumentList">ArgumentList</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-reserved-function-names">xgc: reserved-function-names</a> */</td></tr><tr><td><code><a href="#doc-xpath40-EQName">EQName</a><a href="#doc-xpath40-ArgumentList">ArgumentList</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-reserved-function-names">xgc: reserved-function-names</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-reserved-function-names">xgc: reserved-function-names</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-parens">gn: parens</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-ArgumentList" id="doc-xpath40-ArgumentList"></a>[<span class="deltaxml-old" style="background:#FF5555">156</span><span class="deltaxml-new" style="background:#90EE90">157</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-ArgumentList">ArgumentList</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"(" ((<a href="#doc-xpath40-PositionalArguments">PositionalArguments</a> ("," <a href="#prod-xpath40-KeywordArguments">KeywordArguments</a>)?) | <a href="#prod-xpath40-KeywordArguments">KeywordArguments</a>)? ")"</code></td></tr><tr><td><code>"(" ((<a href="#doc-xpath40-PositionalArguments">PositionalArguments</a> ("," <a href="#prod-xpath40-KeywordArguments">KeywordArguments</a>)?) | <a href="#prod-xpath40-KeywordArguments">KeywordArguments</a>)? ")"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="noid_d4e15609.doc-xpath40-PositionalArguments" id="noid_d4e15609.doc-xpath40-PositionalArguments"></a>[<span class="deltaxml-old" style="background:#FF5555">158</span><span class="deltaxml-new" style="background:#90EE90">159</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-PositionalArguments">PositionalArguments</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>(<a href="#doc-xpath40-Argument">Argument</a> ++ ",")</code></td></tr><tr><td><code>(<a href="#doc-xpath40-Argument">Argument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-Argument" id="doc-xpath40-Argument"></a>[<span class="deltaxml-old" style="background:#FF5555">179</span><span class="deltaxml-new" style="background:#90EE90">180</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-Argument">Argument</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-ExprSingle">ExprSingle</a> | <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td></tr><tr><td><code><a href="#doc-xpath40-ExprSingle">ExprSingle</a> | <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-ArgumentPlaceholder" id="doc-xpath40-ArgumentPlaceholder"></a>[<span class="deltaxml-old" style="background:#FF5555">180</span><span class="deltaxml-new" style="background:#90EE90">181</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"?"</code></td></tr><tr><td><code>"?"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="noid_d4e15612.doc-xpath40-KeywordArguments" id="noid_d4e15612.doc-xpath40-KeywordArguments"></a>[<span class="deltaxml-old" style="background:#FF5555">159</span><span class="deltaxml-new" style="background:#90EE90">160</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-KeywordArguments">KeywordArguments</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>(<a href="#doc-xpath40-KeywordArgument">KeywordArgument</a> ++ ",")</code></td></tr><tr><td><code>(<a href="#doc-xpath40-KeywordArgument">KeywordArgument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-KeywordArgument" id="doc-xpath40-KeywordArgument"></a>[<span class="deltaxml-old" style="background:#FF5555">160</span><span class="deltaxml-new" style="background:#90EE90">161</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-KeywordArgument">KeywordArgument</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-EQName">EQName</a> ":=" <a href="#doc-xpath40-Argument">Argument</a></code></td></tr><tr><td><code><a href="#doc-xpath40-EQName">EQName</a> ":=" <a href="#doc-xpath40-Argument">Argument</a></code></td></tr></tbody></table><p> [<a id="dt-static-function-call" title="static function call">Definition</a>: A <b>static function call</b> consists of an EQName followed by a parenthesized list of zero or more arguments.] </p><p>The argument list consists of zero or more positional arguments, followed by zero or more keyword arguments.</p><p> [<a id="dt-arg-expr" title="argument expression">Definition</a>: An argument to a function call is either an <b>argument expression</b> or an <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a> (<code>?</code>); in both cases it may either be supplied positionally, or identified by a name (called a keyword).] </p><p>This section is concerned with static function calls in which none of the arguments are <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholders</a>. Calls using one or more <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholders</a> are covered in the section <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p>If the function name supplied in a static function call is an unprefixed <a title="lexical QName" class="termref" href="#dt-qname">lexical QName</a>, it is expanded using the <a title="default function namespace" class="termref" href="#dt-default-function-namespace">default function namespace</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a>. </p><p> The <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a> used as the function name and the number of arguments used in the static function call (the required arity) must match the name and arity range of a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a><span> using the rules defined in the previous section</span>; if there is no match, a <a title="static error" class="termref" href="#dt-static-error">static error</a> is raised [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>]. </p><p>Evaluation of static function calls is described in <a href="#id-eval-static-function-call"><b>4.5.1.2 Evaluating Static Function Calls</b></a> .</p><p>Since the arguments of a function call are separated by commas, any <a title="argument expression" class="termref" href="#dt-arg-expr">argument expression</a> that contains a top-level <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a> must be enclosed in parentheses. Here are some illustrative examples of static function calls:</p><ul><li><p><code>my:three-argument-function(1, 2, 3)</code> denotes a static function call with three <span>positional</span> arguments. <span>The corresponding function declaration must define at least three parameters, and may define more, provided they are optional.</span></p></li><li><p><code>my:two-argument-function((1, 2), 3)</code> denotes a static function call with two arguments, the first of which is a sequence of two values. <span>The corresponding function declaration must define at least two parameters, and may define more, provided they are optional.</span></p></li><li><p><code>my:two-argument-function(1, ())</code> denotes a static function call with two arguments, the second of which is an empty sequence.</p></li><li><p><code>my:one-argument-function((1, 2, 3))</code> denotes a static function call with one argument that is a sequence of three values. </p></li><li><p><code>my:one-argument-function(( ))</code> denotes a static function call with one argument that is an empty sequence.</p></li><li><p><code>my:zero-argument-function( )</code> denotes a static function call with zero arguments.</p></li><li><p><code>lang(node := $n, language := 'de')</code> is a static function call with two keyword arguments. The corresponding function declaration defines two parameters, a required parameter <code>language</code> and an optional parameter <code>node</code>. This call supplies values for both parameters. It is equivalent to the call <code>fn:lang('de', $n)</code>. Note that the keyword arguments are in a different order from the parameter declarations. </p></li><li><p><code>sort(//employee, key := fn($e) { xs:decimal($e/salary) })</code> is a static function call with one positional argument and one keyword argument. The corresponding function declaration defines three parameters, a required parameter <code>$input</code>, an optional parameter <code>$collation</code>, and an optional parameter <code>$key</code> This call supplies values for the first and third parameters, leaving the second parameter (<code>$collation</code>) to take its default value. The default value of the <code>$collation</code> parameter is given as <code>fn:default-collation()</code>, so the value supplied to the function is the default collation from the dynamic context of the caller. It is equivalent to the call <code>fn:sort(//employee, fn:default-collation(), fn($e) { xs:decimal($e/salary) })</code>. </p></li></ul><p>An <code>EQName</code> in a <code>KeywordArgument</code> is expanded to a QName value; if there is no prefix, then the name is in no namespace (otherwise the prefix is resolved in the usual way). The keywords used in a function call (after expansion to QNames) must be distinct [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>]; [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>].</p></div><div class="div4"><h5><a id="id-eval-static-function-call"></a>4.5.1.2 Evaluating Static Function Calls</h5><p>This section applies to static function calls where none of the arguments is an <code>ArgumentPlaceholder</code>. For function calls involving placeholders, see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p> When a static function call <var>FC</var> is evaluated with respect to a static context <var>SC</var> and a dynamic context <var>DC</var>, the result is obtained as follows: </p><ol class="enumar"><li><p> The <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> to be used is found in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a> of <var>SC</var>. </p><p>The <b>required arity</b> is the total number of arguments in the function call, including both positional and keyword arguments.</p><p> There can be at most one <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a> component of <var>SC</var> whose function name matches the expanded QName in <var>FC</var> and whose <a title="arity range" class="termref" href="#dt-arity-range">arity range</a> includes the arity of <var>FC</var>’s <code>ArgumentList</code>. </p><p>If there is no such <a title="function definition" class="termref" href="#dt-function-definition">function definition</a>, a static error [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>] is raised.</p></li><li><p>Each parameter in the <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> is matched to an argument expression as follows:</p><ol class="enumla"><li><p>If there are <var>N</var> positional arguments in the function call <var>FC</var>, then the corresponding argument expressions are matched pairwise to the first <var>N</var> parameters in the declaration. For this purpose the required parameters and optional parameters in <var>FD</var> are concatenated into a single list, in order.</p></li><li><p>Any keyword arguments in <var>FC</var> are then matched to parameters (whether required or optional) in <var>FD</var> by comparing the keyword used in <var>FC</var> with the paramater name declared in <var>FD</var>. Each keyword must match the name of a declared parameter [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>], and this must be one that has not already been matched to a positional argument. [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>].</p></li><li><p>If any required parameter has not been matched to any argument in <var>FC</var> by applying the above rules, a static error is reported [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>] </p></li><li><p>If any optional parameter has not been matched to any argument in <var>FC</var> by applying the above rules, then the parameter is matched to the default value expression for that parameter in <var>FD</var>.</p></li></ol></li><li><p> Each argument expression established by the above rules is evaluated with respect to DC. The order of argument evaluation is <a title="implementation   dependent" class="termref" href="#dt-implementation-dependent">implementation dependent</a> and it is not required that an argument be evaluated if the function body can be evaluated without evaluating that argument.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>All argument expressions, including default value expressions, are evaluated in the dynamic context of the function call. It is therefore possible to use a default value expression such as <code>.</code>, or <code>/</code>, or <code>fn:current-dateTime()</code>, whose value depends on the dynamic context of the function call.</p></div><p>If the expression used for the default value of a parameter has no dependencies on the dynamic context, then an implementation <span class="verb">may</span> choose to reuse the same value on repeated function calls rather than re-evaluating it on each function call.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>This is relevant, for example, if the expression constructs new nodes.</p></div></li><li><p>The result of evaluating the argument expression is converted to the required type (the declared type associated with the corresponding parameter in the function declaration, defaulting to <code>item()*</code>) by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>.</p><p><span>This applies both to explicitly supplied arguments, and to values obtained by evaluating default value expressions. In both cases a type error will be raised if the value (after coercion) does not match the required type.</span></p></li><li><p>The result of the function call is obtained as follows:</p><ul><li><p><var>FD</var>’s <span>body</span> is invoked in an implementation-dependent way. The processor makes the following information available to that invocation: </p><ul><li><p>The converted argument values;</p></li><li><p>If the function is <a title="context dependent" class="termref" href="#dt-context-dependent">context dependent</a>, the static context <var>SC</var> and dynamic context <var>DC</var> of the function call. </p></li></ul></li><li><p>The result is converted to the required type (the declared return type in the function declaration, defaulting to <code>item()*</code>) by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>.</p><p>The result of applying the coercion rules is either an instance of <var>FD</var>’s return type or a dynamic error. This result is then the result of evaluating <var>FC</var>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>A host language may define alternative rules for processing the result, especially in the case of external functions implemented using a non-XDM type system.</p></div></li><li><p> Errors raised by system functions are defined in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>. </p></li><li class="xquery"><p> Errors raised by external functions are <a title="implementation defined" class="termref" href="#dt-implementation-defined">implementation-defined</a> (see <a href="#id-consistency-constraints"><b>2.3.6 Consistency Constraints</b></a>). </p></li><li class="xpath"><p> Errors raised by host-language-dependent functions are <a title="implementation defined" class="termref" href="#dt-implementation-defined">implementation-defined</a>. </p></li></ul><div class="example"><div class="exampleHeader"><a id="d5e17270"></a>Example: A System Function</div><p>The following function call uses the function <a href="https://qt4cg.org/specifications/xpath-functions-40/#func-base-uri">Section 2.1.5 fn:base-uri</a><sup><small>FO</small></sup>. Use of <code>SC</code> and <code>DC</code> and errors raised by this function are all defined in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>.</p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">base-uri()</pre></div></div></div></li></ol></div></div><div class="div3"><h4><a id="id-dynamic-functions"></a>4.5.2 Function Items</h4><p>A <a title="function item" class="termref" href="#dt-function-item">function item</a> is an XDM value that can be bound to a variable, or manipulated in various ways by XQuery 4.0 and XPath 4.0 expressions. The most significant such expression is a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-call">dynamic function call</a>, which supplies values of arguments and evaluates the function to produce a result.</p><p>The syntax of dynamic function calls is defined in <a href="#id-dynamic-function-invocation"><b>4.5.2.1 Dynamic Function Calls</b></a>.</p><p>A number of constructs can be used to produce a <a title="function item" class="termref" href="#dt-function-item">function item</a>, notably:</p><ul><li><p>A <b>named function reference</b> (see <a href="#id-named-function-ref"><b>4.5.2.4 Named Function References</b></a>) constructs a function item by reference to <a title="function definition" class="termref" href="#dt-function-definition">function definitions</a> in the static context. For example, <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-node-name"><code>fn:node-name#1</code></a> returns a function item whose effect is to call the static <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-node-name"><code>fn:node-name</code></a> function with one argument.</p></li><li><p>An <b>inline function</b> (see <a href="#id-inline-func"><b>4.5.2.5 Inline Function Expressions</b></a> ) constructs a function item whose <span>body</span> is defined locally. For example, the construct <code>fn($x) { $x + 1 }</code> returns a function item whose effect is to increment the value of the supplied argument.</p></li><li><p>A <b>partial function application</b> (see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>) derives one function item from another by supplying the values of some of its arguments. For example, <code>fn:ends-with(?, ".txt")</code> returns a function item with one argument that tests whether the supplied string ends with the substring <code>".txt"</code>.</p></li><li><p>Maps and arrays are also function items. See <a href="#id-map-constructors"><b>4.14.1.1 Map Constructors</b></a> and <a href="#id-array-constructors"><b>4.14.2.1 Array Constructors</b></a>.</p></li><li><p>The <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-function-lookup"><code>fn:function-lookup</code></a> function can be called to discover functions that are present in the <a title="dynamic context" class="termref" href="#dt-dynamic-context">dynamic context</a>.</p></li><li><p>The <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-load-xquery-module"><code>fn:load-xquery-module</code></a> function can be called to load functions dynamically from an external XQuery library module.</p></li><li><p>Some system functions such as <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-random-number-generator"><code>fn:random-number-generator</code></a> and <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-op"><code>fn:op</code></a> return a <a title="function item" class="termref" href="#dt-function-item">function item</a> as their result.</p></li></ul><p>These constructs are described in detail in the following sections, or in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>.</p><div class="div4"><h5><a id="id-dynamic-function-invocation"></a>4.5.2.1 Dynamic Function Calls</h5><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-DynamicFunctionCall" id="doc-xpath40-DynamicFunctionCall"></a>[<span class="deltaxml-old" style="background:#FF5555">155</span><span class="deltaxml-new" style="background:#90EE90">156</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-DynamicFunctionCall">DynamicFunctionCall</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-PositionalArgumentList">PositionalArgumentList</a></code></td></tr><tr><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-PositionalArgumentList">PositionalArgumentList</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-PositionalArgumentList" id="doc-xpath40-PositionalArgumentList"></a>[<span class="deltaxml-old" style="background:#FF5555">157</span><span class="deltaxml-new" style="background:#90EE90">158</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-PositionalArgumentList">PositionalArgumentList</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"(" <a href="#doc-xpath40-PositionalArguments">PositionalArguments</a>? ")"</code></td></tr><tr><td><code>"(" <a href="#doc-xpath40-PositionalArguments">PositionalArguments</a>? ")"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-PositionalArguments" id="doc-xpath40-PositionalArguments"></a>[<span class="deltaxml-old" style="background:#FF5555">158</span><span class="deltaxml-new" style="background:#90EE90">159</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-PositionalArguments">PositionalArguments</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>(<a href="#doc-xpath40-Argument">Argument</a> ++ ",")</code></td></tr><tr><td><code>(<a href="#doc-xpath40-Argument">Argument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="noid_d4e16127.doc-xpath40-Argument" id="noid_d4e16127.doc-xpath40-Argument"></a>[<span class="deltaxml-old" style="background:#FF5555">179</span><span class="deltaxml-new" style="background:#90EE90">180</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-Argument">Argument</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-ExprSingle">ExprSingle</a> | <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td></tr><tr><td><code><a href="#doc-xpath40-ExprSingle">ExprSingle</a> | <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="noid_d4e16128.doc-xpath40-ArgumentPlaceholder" id="noid_d4e16128.doc-xpath40-ArgumentPlaceholder"></a>[<span class="deltaxml-old" style="background:#FF5555">180</span><span class="deltaxml-new" style="background:#90EE90">181</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"?"</code></td></tr><tr><td><code>"?"</code></td></tr></tbody></table><p> [<a id="dt-dynamic-function-invocation" title="dynamic function call">Definition</a>: A <b>dynamic function call</b> consists of a base expression that returns the function and a parenthesized list of zero or more arguments (<a title="argument expression" class="termref" href="#dt-arg-expr">argument expressions</a> or ArgumentPlaceholders).] </p><p> A dynamic function call is evaluated as described in <a href="#id-eval-dynamic-function-call"><b>4.5.2.2 Evaluating Dynamic Function Calls</b></a>. </p><p>The following are examples of some dynamic function calls:</p><ul><li><p>This example calls the function contained in <code>$f</code>, passing the arguments 2 and 3: </p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">$f(2, 3)</pre></div></div></li><li><p>This example fetches the second item from sequence <code>$f</code>, treats it as a function and calls it, passing an <code>xs:string</code> argument: </p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">$f[2]("Hi there")</pre></div></div></li><li><p>This example calls the function <code>$f</code> passing no arguments, and filters the result with a positional predicate: </p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">$f()[2]</pre></div></div></li></ul><div class="note"><p class="prefix"><b>Note:</b></p><p>Arguments in a dynamic function call are always supplied positionally.</p></div></div><div class="div4"><h5><a id="id-eval-dynamic-function-call"></a>4.5.2.2 Evaluating Dynamic Function Calls</h5><p>This section applies to dynamic function calls whose arguments do not include an <code>ArgumentPlaceholder</code>. For function calls that include a placeholder, see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p> [<a id="dt-dynamic-function-call" title="dynamic function call">Definition</a>: A <b>dynamic function call</b> is an expression that is evaluated by calling a <a title="function item" class="termref" href="#dt-function-item">function item</a>, which is typically obtained dynamically.] </p><p> When a dynamic function call <var>FC</var> is evaluated, the result is obtained as follows: </p><ol class="enumar"><li><p> The <a title="function item" class="termref" href="#dt-function-item">function item</a><var>FI</var> to be called is obtained by evaluating the base expression of the function call. If this yields a sequence consisting of a single function item whose arity matches the number of arguments in the <code>ArgumentList</code>, let <var>FI</var> denote that function item. Otherwise, a type error is raised [<a href="#ERRXPTY0004" title="err:XPTY0004">err:XPTY0004</a>]. </p><div class="note"><p class="prefix"><b>Note:</b></p><p>Keyword arguments are not allowed in a dynamic function call.</p></div></li><li><p><a title="argument expression" class="termref" href="#dt-arg-expr">Argument expressions</a> are evaluated, producing <b>argument values</b>. The order of argument evaluation is <a title="implementation   dependent" class="termref" href="#dt-implementation-dependent">implementation-dependent</a> and an argument need not be evaluated if the function body can be evaluated without evaluating that argument.</p></li><li><p> Each argument value is converted to the corresponding parameter type in <var>FI</var>’s signature by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>, resulting in a <b>converted argument value</b></p></li><li><p>If <var>FI</var> is a map, it is evaluated as described in <a href="#id-map-lookup"><b>4.14.1.2 Maps as Functions</b></a>.</p></li><li><p>If <var>FI</var> is an array, it is evaluated as described in <a href="#id-array-lookup"><b>4.14.2.2 Arrays as Functions</b></a>.</p></li><li><p> If <var>FI</var>’s <span>body</span> is an XQuery 4.0 and XPath 4.0 expression (for example, if <var>FI</var> is <span class="xquery"><span class="xquery">a <a title="user-defined function" class="termref" href="#dt-udf">user-defined function</a> or</span></span> an <a title="anonymous function" class="termref" href="#dt-anonymous-function">anonymous function</a>, or a <a title="partially applied function" class="termref" href="#dt-partially-applied-function">partial application</a> of such a function): </p><ol class="enumla"><li><p><var>FI</var>’s <span>body</span> is evaluated. The static context for this evaluation is the static context of the XQuery 4.0 and XPath 4.0 expression. The dynamic context for this evaluation is obtained by taking the dynamic context of the <span class="xquery"><span class="xquery">module</span></span><span class="xpath"><span class="xpath"><code>InlineFunctionExpr</code></span></span> that contains the <code>FunctionBody</code>, and making the following changes: </p><ul><li><p> The <a title="focus" class="termref" href="#dt-focus">focus</a> (context value, context position, and context size) is <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#dt-absent">absent</a><sup><small>DM</small></sup>. </p></li><li><p> In the <a title="variable values" class="termref" href="#dt-variable-values">variable values</a> component of the dynamic context, each converted argument value is bound to the corresponding parameter name. </p><p><span>When this is done, the converted argument values retain their <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic types</a>, even where these are <a title="subtype" class="termref" href="#dt-subtype">subtypes</a> of the declared parameter types.</span> For example, a function with a parameter <code>$p</code> of type <code>xs:decimal</code> can be called with an argument of type <code>xs:integer</code>, which is derived from <code>xs:decimal</code>. During the processing of this function call, the value of <code>$p</code> inside the body of the function retains its <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic type</a> of <code>xs:integer</code>. </p></li><li><p><var>FI</var>’s nonlocal variable bindings are also added to the <a title="variable values" class="termref" href="#dt-variable-values">variable values</a>. (Note that the names of the nonlocal variables are by definition disjoint from the parameter names, so there can be no conflict.) </p></li></ul></li><li><p> The value returned by evaluating the function body is then converted to the declared return type of <var>FI</var> by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>. The result is then the result of evaluating <var>FC</var>. </p><p> As with argument values, the value returned by a function retains its <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic type</a>, which may be a <a title="subtype" class="termref" href="#dt-subtype">subtype</a> of the declared return type of <var>FI</var>. For example, a function that has a declared return type of <code>xs:decimal</code> may in fact return a value of dynamic type <code>xs:integer</code>. </p></li></ol><div class="example"><div class="exampleHeader"><a id="d5e17663"></a>Example: Derived Types and Nonlocal Variable Bindings</div><p><code>$incr</code> is a nonlocal variable that is available within the function because its variable binding has been added to the variable values of the function.. Even though the parameter and return type of this function are both <code>xs:decimal</code>, the more specific type <code>xs:integer</code> is preserved in both cases.</p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">let $incr := 1
+return $f(12.3)</pre></div></div><div class="xquery"><p class="xquery">With XQuery 4.0, as a consequence of function coercion, this fails with a type error because the argument supplied in the function call is not of type <code>xs:integer</code>.</p></div></div></div><div class="div3"><h4><a id="id-coercion-examples"></a>3.4.5 Examples of Coercions</h4><p>This section illustrates the effect of the coercion rules with examples.</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-string"></a>Example: Coercion to <code>xs:string</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:string</code>. For example, the second argument of <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-matches"><code>fn:matches</code></a>, which expects a regular expression. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><div class="medium"><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>"[0-9]"</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>default-language()</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of <code>xs:language</code>, which is a subtype of the required type <code>xs:string</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;[0-9]&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. Unless it has been schema-validated, the typed value will be an instance of <code>xs:untypedAtomic</code>, which is accepted when the required type is <code>xs:string</code>.</p><p>Supplying an element whose type annotation is (say) <code>xs:date</code> will fail with a type error.</p><div class="xpath"><p class="xpath">The effect is subtly different if XPath 1.0 compatibility mode is enabled. In this case coercion takes the string value of the element node. This differs from the typed value only in the case where the element has been schema-validated and has a type annotation other than <code>xs:string</code>.</p></div></td></tr><tr><td style="vertical-align:top"><code>xs:anyURI("urn:dummy")</code></td><td style="vertical-align:top"><p>Supplying an instance of <code>xs:anyURI</code> where the expected type is <code>xs:string</code> is permitted; this is one of the pairs of types where implicit casting is allowed.</p></td></tr><tr class="xpath"><td style="vertical-align:top"><code>17.2</code></td><td style="vertical-align:top"><p>Supplying a number where a string is expected raises a type error.</p><div class="xpath"><p class="xpath">However, if XPath 1.0 compatibility mode is enabled, the number is converted to a string as if by the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-string"><code>fn:string</code></a> function.</p></div></td></tr><tr class="xpath"><td style="vertical-align:top"><code>//author/@id</code></td><td style="vertical-align:top"><p>Supplying a sequence of nodes where a single string is expected will raise a type error unless either there is only one node in the sequence. In this case the typed value of the node will be used (this must be of type <code>xs:string</code>, <code>xs:untypedAtomic</code>, or <code>xs:anyURI</code>).</p><div class="xpath"><p class="xpath">If XPath 1.0 compatibility mode is enabled, however, all strings after the first are discarded, and the string value of the first node is used; if the sequence is empty, a zero-length string is supplied.</p></div></td></tr><tr class="xpath"><td style="vertical-align:top"><code>("red", "green", "blue")</code></td><td style="vertical-align:top"><p>Supplying a sequence of strings where a single string is expected raises a type error.</p><div class="xpath"><p class="xpath">If XPath 1.0 compatibility mode is enabled, however, all strings after the first are discarded; the effect is as if the supplied value were <code>"red"</code>.</p></div></td></tr><tr class="xpath"><td style="vertical-align:top"><code>()</code></td><td style="vertical-align:top"><p>Supplying an empty sequence where a single string is expected will fail.</p><div class="xpath"><p class="xpath">If XPath 1.0 compatibility mode is enabled, however, the value is coerced by applying the function <code>fn:string(())</code>, which delivers the zero-length string.</p></div></td></tr><tr><td style="vertical-align:top"><code>["a|b"]</code></td><td style="vertical-align:top"><p>Supplying an array holding a single string succeeds, because the rules cause the array to be atomized, and the value after atomization is a single string.</p><p>Supplying an array holding multiple strings would fail.</p><div class="xpath"><p class="xpath">In XPath 1.0 compatibility mode, supplying an array will fail, regardless of the array contents, because the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-string"><code>fn:string</code></a> function does not accept arrays.</p></div></td></tr></tbody></table></div></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-decimal"></a>Example: Coercion to <code>xs:decimal?</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:decimal?</code>. For example, the first argument of <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-seconds"><code>fn:seconds</code></a>, which expects a decimal number of seconds. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><div class="medium"><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>12.4</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>()</code></td><td style="vertical-align:top"><p>None; an empty sequence is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>42</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of <code>xs:integer</code>, which is a subtype of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>math:pi()</code></td><td style="vertical-align:top"><p>The supplied value is an instance of <code>xs:double</code>, which can be converted to <code>xs:decimal</code> under the coercion rules.</p></td></tr><tr><td style="vertical-align:top"><code>("a", "b")[.="c"]</code></td><td style="vertical-align:top"><p>The supplied value is an empty sequence, which is a valid instance of the required type <code>xs:decimal?</code>. However, the processor may (optionally) reject this as an implausible coercion, on the grounds that it can only succeed in one special case, namely where the filter expression selects no values. </p></td></tr><tr><td style="vertical-align:top"><code>(1.5, 2.5, 3.5)</code></td><td style="vertical-align:top"><p>A type error is raised<span class="xpath"><span class="xpath">, except in the case where XPath 1.0 compatibility is enabled, in which case all values after the first are discarded</span></span>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;3.14159&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The element node is atomized; unless it has been schema-validated, the result will be <code>"3.14159"</code> as an instance of <code>xs:untypedAtomic</code>. This is converted to an instance of <code>xs:decimal</code> following the rules of the <code>cast as</code> operator.</p></td></tr><tr class="xpath"><td style="vertical-align:top"><code>"12.2"</code></td><td style="vertical-align:top"><p>Supplying a string where an <code>xs:decimal</code> is a type error<span class="xpath"><span class="xpath">, even if XPath 1.0 compatibility mode is enabled. The rules for compatibility mode would allow conversion if the required type were <code>xs:double</code>, but not for <code>xs:decimal</code></span></span>. </p></td></tr><tr><td style="vertical-align:top"><code>[1.5]</code></td><td style="vertical-align:top"><p>The array is atomized, and the result is a valid instance of the required type <code>xs:decimal?</code></p></td></tr><tr><td style="vertical-align:top"><code>[]</code></td><td style="vertical-align:top"><p>The array is atomized, and the result is an empty sequence, which is a valid instance of the required type <code>xs:decimal?</code></p></td></tr></tbody></table></div></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-positive-integer"></a>Example: Coercion to <code>xs:positive-integer</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:positive-integer</code>. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><div class="medium"><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>12</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:integer</code>. Because the supplied value and the required type, <code>xs:positiveInteger</code>, both come under the primitive type <code>xs:decimal</code>, and the value <code>12</code> is within the value space of <code>xs:positiveInteger</code>, the value is relabeled as an <code>xs:positiveInteger</code> and the call succeeds.</p></td></tr><tr><td style="vertical-align:top"><code>12.1</code></td><td style="vertical-align:top"><p>This fails with a type error, because the <code>xs:decimal</code> value <code>12.1</code> is not a value in the value space of <code>xs:positiveInteger</code>. This is so even though casting to <code>xs:positiveInteger</code> would succeed.</p></td></tr><tr><td style="vertical-align:top"><code>math:pi()</code></td><td style="vertical-align:top"><p>This fails with a type error. A value of type <code>xs:double</code> is accepted where the required type is <code>xs:decimal</code> or <code>xs:float</code>, but not where it is <code>xs:positiveInteger</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;1200&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. If the element has not been schema-validated, the result will be an <code>xs:untypedAtomic</code> item, which is successfully cast to the required type <code>xs:positiveInteger</code>. If the element has been validated against a schema, then coercion succeeds if the typed value would itself be acceptable, for example if it is an <code>xs:positiveInteger</code>, or some other <code>xs:decimal</code> within the value space of <code>xs:positiveInteger</code>.</p></td></tr></tbody></table></div></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-union"></a>Example: Coercion to a union type</div><p>Consider the first parameter of the function <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a>, whose declared type is <code>(xs:string | xs:positiveInteger)</code>. The rules are the same as if it were a union typed declared in an imported schema.</p><div class="medium"><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>"amp"</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:string</code>, which is one of the allowed types. The call therefore succeeds.</p></td></tr><tr><td style="vertical-align:top"><code>"#"</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:string</code>, which is one of the allowed types. As far as the coercion rules are concerned, the call therefore succeeds. Under the semantic rules for the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a> function, however, this value is not accepted; a dynamic error (as distinct from a type error) is therefore raised.</p></td></tr><tr><td style="vertical-align:top"><code>0x25</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:integer</code>. Although this is not one of the allowed types, it is acceptable because coercion of the value to type <code>xs:positiveInteger</code> succeeds. The value is relabeled as an instance of <code>xs:positiveInteger</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;0x25&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. Assuming that the node has not been schema-validated, the result is an instance of <code>xs:untypedAtomic</code>. The member types of the choice are tested in order. Conversion to <code>xs:string</code> with the value "0x25" succeeds, so the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a> function is called supplying this string; but the function rejects this string as semantically invalid. The same would happen if the value were, say, &lt;a&gt;37&lt;/a&gt;. Supplying such a value requires an explicit cast, for example <code>fn:char( xs:positiveInteger( ./a ))</code>.</p></td></tr></tbody></table></div></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-choice"></a>Example: Coercion to a choice type</div><p>Suppose the required type is <code>(record(x as xs:decimal, y as xs:decimal, *) | record(size as enum("S", "M", "L", "XL"), *))</code>.</p><div class="medium"><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>{ "x": 1, "y": 2, "z": 3 }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of the first record type: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "size": "M" }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of the second record type: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1, "y": 2, "size": "XL" }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of both record types: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1e0, "y": 2e0, "size": "XL" }</code></td><td style="vertical-align:top"><p>The supplied value is not an instance of the first record type because the fields are of type <code>xs:double</code> rather than <code>xs:decimal</code>. It is however an instance of the second record type. It is therefore accepted <em>as is</em>; the fields <code>x</code> and <code>y</code> are not converted from <code>xs:double</code> to <code>xs:decimal</code>.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1e0, "y": 2e0, "size": "XXL" }</code></td><td style="vertical-align:top"><p>The supplied value is not an instance of the first record type because the fields are of type <code>xs:double</code> rather than <code>xs:decimal</code>, and it is not an instance of the second record type because the <code>size</code> value does not match the enumeration type. Coercion is therefore attempted to the first record type, and succeeds. The <code>x</code> and <code>y</code> fields are coerced to <code>xs:decimal</code>, and the <code>size</code> field is accepted <em>as is</em>.</p></td></tr></tbody></table></div></div></div></div><div class="div2"><h3><a id="id-predefined-types"></a>3.5 Schema Types</h3><p> [<a id="dt-schema-type" title="schema type">Definition</a>: A <b>schema type</b> is a complex type or simple type as defined in the <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> specifications, including built-in types as well as user-defined types.] </p><p>Every schema type is either a <b>complex type</b> or a <b>simple type</b>; simple types are further subdivided into <b>list types</b>, <b>union types</b>, and <b>atomic types</b> (see <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> for definitions and explanations of these terms.)</p><p>A schema type can appear as a type annotation on an element or attribute node. The type annotation on an element node can be a complex type or a simple type; the type annotation on an attribute node is always a simple type. Non-instantiable types such as <code>xs:NOTATION</code> or <code>xs:anyAtomicType</code> never appear as type annotations, but their derived types can be so used. Union types never appear as type annotations; when an element or attribute is validated against a union type, the resulting type annotation will be one of the types in the transitive membership of the union type.</p><p> [<a id="dt-atomic-type" title="atomic type">Definition</a>: An <b>atomic type</b> is a simple <a title="schema type" class="termref" href="#dt-schema-type">schema type</a> whose <a href="https://www.w3.org/TR/xmlschema11-1/#std-variety">{variety}<sup><small>XS11-1</small></sup></a> is <code>atomic</code>.] </p><p>An <b>atomic type</b> is either a built-in atomic type (defined either in the XSD specification or in this specification), or it is a user-defined atomic type included in an imported schema.</p><div class="xpath"><p class="xpath">The <a title="in-scope schema type" class="termref" href="#dt-is-types">in-scope schema types</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a> are initialized with a set of predefined schema types that is determined by the host language. This set may include some or all of the schema types in the namespace <code>http://www.w3.org/2001/XMLSchema</code>, represented in this document by the namespace prefix <code>xs</code>. The schema types in this namespace are defined in <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> and augmented by additional types defined in <a href="#xpath-datamodel-40">[XQuery and XPath Data Model (XDM) 4.0]</a>. An implementation that has based its type system on <a href="#XMLSchema10">[XML Schema 1.0]</a> is not required to support the <code>xs:dateTimeStamp</code> or <code>xs:error</code> types.</p></div><p>The schema types defined in <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#types-predefined">Section 2.8.3 Predefined Types</a><sup><small>DM</small></sup> are summarized below.</p><div class="xquery"><p class="xquery">The <a title="in-scope schema type" class="termref" href="#dt-is-types">in-scope schema types</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a> are initialized with certain predefined schema types, including the built-in schema types in the namespace <code>http://www.w3.org/2001/XMLSchema</code>, which has the predefined namespace prefix <code>xs</code>. The schema types in this namespace are defined in <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> and augmented by additional types defined in <a href="#xpath-datamodel-40">[XQuery and XPath Data Model (XDM) 4.0]</a>. Element and attribute declarations in the <code>xs</code> namespace are not implicitly included in the static context. The schema types defined in <a href="#xpath-datamodel-40">[XQuery and XPath Data Model (XDM) 4.0]</a> are summarized below.</p></div><ol class="enumar"><li><p> [<a id="dt-untyped" title="xs:untyped">Definition</a>: <code>xs:untyped</code> is used as the <a title="type annotation" class="termref" href="#dt-type-annotation">type annotation</a> of an element node that has not been validated, or has been validated in <code>skip</code> mode.] No predefined schema types are derived from <code>xs:untyped</code>.</p></li><li><p> [<a id="dt-untypedAtomic" title="xs:untypedAtomic">Definition</a>: <code>xs:untypedAtomic</code> is an <a title="atomic type" class="termref" href="#dt-atomic-type">atomic type</a> that is used to denote untyped atomic data, such as text that has not been assigned a more specific type.] An attribute that has been validated in <code>skip</code> mode is represented in the <a title="data model" class="termref" href="#dt-datamodel">data model</a> by an attribute node with the <a title="type annotation" class="termref" href="#dt-type-annotation">type annotation</a><code>xs:untypedAtomic</code>. No predefined schema types are derived from <code>xs:untypedAtomic</code>.</p></li><li><p> [<a id="dt-dayTimeDuration" title="xs:dayTimeDuration">Definition</a>: <code>xs:dayTimeDuration</code> is derived by restriction from <code>xs:duration</code>. The lexical representation of <code>xs:dayTimeDuration</code> is restricted to contain only day, hour, minute, and second components.] </p></li><li><p> [<a id="dt-yearMonthDuration" title="xs:yearMonthDuration">Definition</a>: <code>xs:yearMonthDuration</code> is derived by restriction from <code>xs:duration</code>. The lexical representation of <code>xs:yearMonthDuration</code> is restricted to contain only year and month components.] </p></li><li><p> [<a id="dt-anyAtomicType" title="xs:anyAtomicType">Definition</a>: <code>xs:anyAtomicType</code> is an <a title="atomic type" class="termref" href="#dt-atomic-type">atomic type</a> that includes all atomic items (and no values that are not atomic). Its base type is <code>xs:anySimpleType</code> from which all simple types, including atomic, list, and union types, are derived. All primitive atomic types, such as <code>xs:decimal</code> and <code>xs:string</code>, have <code>xs:anyAtomicType</code> as their base type.] </p><div class="note"><p class="prefix"><b>Note:</b></p><p><code>xs:anyAtomicType</code> will not appear as the type of an actual value in an <a title="XDM instance" class="termref" href="#dt-data-model-instance">XDM instance</a>.</p></div></li><li><p> [<a id="dt-xs-error" title="xs:error">Definition</a>: <code>xs:error</code> is a simple type with no value space. It is defined in <a href="https://www.w3.org/TR/xmlschema11-1/#xsd-error">Section 3.16.7.3 xs:error </a><sup><small>XS11-1</small></sup> and can be used in the <a href="#id-sequencetype-syntax"><b>3.1 Sequence Types</b></a> to raise errors.] </p></li></ol><p>The relationships among the schema types in the <code>xs</code> namespace are illustrated in Figure 2. A more complete description of the XQuery 4.0 and XPath 4.0 type hierarchy can be found in <a href="https://qt4cg.org/specifications/xpath-functions-40/#datatypes">Section 1.8 Type System</a><sup><small>FO</small></sup>.</p><img src="types.jpg" alt="Type Hierarchy Diagram"><p>Figure 2: Hierarchy of Schema Types used in XQuery 4.0 and XPath 4.0.</p></div></div><div class="div1"><h2><a id="id-expressions"></a>4 Expressions</h2><p>This section discusses each of the basic kinds of expression. Each kind of expression has a name such as <code>PathExpr</code>, which is introduced on the left side of the grammar production that defines the expression. Since XQuery 4.0 and XPath 4.0 is a composable language, each kind of expression is defined in terms of other expressions whose operators have a higher precedence. In this way, the precedence of operators is represented explicitly in the grammar.</p><p>The order in which expressions are discussed in this document does not reflect the order of operator precedence. In general, this document introduces the simplest kinds of expressions first, followed by more complex expressions. For the complete grammar, see Appendix [<a href="#nt-bnf"><b>A XQuery 4.0 and XPath 4.0 Grammar</b></a>].</p><p><span class="xpath"><span class="xpath">The highest-level symbol in the XPath grammar is XPath.</span></span><span class="xquery"><span class="xquery"> [<a id="dt-query" title="query">Definition</a>: A <b>query</b> consists of one or more <a title="module" class="termref" href="#dt-module">modules</a>.] If a query is executable, one of its modules has a <a title="query body" class="termref" href="#dt-queryBody">Query Body</a> containing an expression whose value is the result of the query. An expression is represented in the XQuery grammar by the symbol <a href="#doc-xpath40-Expr">Expr</a>.</span></span></p><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-XPath" id="doc-xpath40-XPath"></a>[1]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-XPath">XPath</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-Expr">Expr</a></code></td></tr><tr><td><code><a href="#doc-xpath40-Expr">Expr</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-Expr" id="doc-xpath40-Expr"></a>[46]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-Expr">Expr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>(<a href="#doc-xpath40-ExprSingle">ExprSingle</a> ++ ",")</code></td></tr><tr><td><code>(<a href="#doc-xpath40-ExprSingle">ExprSingle</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-ExprSingle" id="doc-xpath40-ExprSingle"></a>[47]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-ExprSingle">ExprSingle</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><span style="display: none;" class="delete_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xpath40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xpath40-OrExpr">OrExpr</a></code></span><span style="display: none;" class="add_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xpath40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xpath40-PipelineExpr">PipelineExpr</a></code></span><span class="modify_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xpath40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xpath40-OrExpr"><span class="deltaxml-old" style="background:#FF5555">OrExpr</span></a><a href="#doc-xpath40-PipelineExpr"><span class="deltaxml-new" style="background:#90EE90">PipelineExpr</span></a></code></span></td></tr><tr><td><span style="display: none;" class="delete_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xpath40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xpath40-OrExpr">OrExpr</a></code></span><span style="display: none;" class="add_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xpath40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xpath40-PipelineExpr">PipelineExpr</a></code></span><span class="modify_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xpath40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xpath40-OrExpr"><span class="deltaxml-old" style="background:#FF5555">OrExpr</span></a><a href="#doc-xpath40-PipelineExpr"><span class="deltaxml-new" style="background:#90EE90">PipelineExpr</span></a></code></span></td></tr></tbody></table><p>The XQuery 4.0 and XPath 4.0 operator that has lowest precedence is the <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a>, which is used to combine two operands to form a sequence. As shown in the grammar, a general expression (<a href="#doc-xpath40-Expr">Expr</a>) can consist of multiple <a href="#doc-xpath40-ExprSingle">ExprSingle</a> operands, separated by commas.</p><p>The name <a href="#doc-xpath40-ExprSingle">ExprSingle</a> denotes an expression that does not contain a top-level <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a> (despite its name, an <a href="#doc-xpath40-ExprSingle">ExprSingle</a> may evaluate to a sequence containing more than one item.)</p><p>The symbol <a href="#doc-xpath40-ExprSingle">ExprSingle</a> is used in various places in the grammar where an expression is not allowed to contain a top-level comma. For example, each of the arguments of a function call must be a <a href="#doc-xpath40-ExprSingle">ExprSingle</a>, because commas are used to separate the arguments of a function call.</p><p><span style="display: none;" class="delete_version">After the comma, the expressions that have next lowest precedence are <span class="xquery"><span class="xquery"><a href="#doc-xpath40-FLWORExpr">FLWORExpr</a>,</span></span><span class="xpath"><span class="xpath"><a href="#doc-xpath40-ForExpr">ForExpr</a>, <a href="#doc-xpath40-LetExpr">LetExpr</a>, </span></span><a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a>, <span class="xquery"><span class="xquery"><a href="#doc-xpath40-SwitchExpr">SwitchExpr</a>, <a href="#doc-xpath40-TypeswitchExpr">TypeswitchExpr</a>, </span></span><a href="#doc-xpath40-IfExpr">IfExpr</a>, <span class="xquery"><span class="xquery"><a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a>, </span></span> and <a href="#doc-xpath40-OrExpr">OrExpr</a>. Each of these expressions is described in a separate section of this document.</span><span style="display: none;" class="add_version">After the comma, the expressions that have next lowest precedence are <span class="xquery"><span class="xquery"><a href="#doc-xpath40-FLWORExpr">FLWORExpr</a>,</span></span><span class="xpath"><span class="xpath"><a href="#doc-xpath40-ForExpr">ForExpr</a>, <a href="#doc-xpath40-LetExpr">LetExpr</a>, </span></span><a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a>, <span class="xquery"><span class="xquery"><a href="#doc-xpath40-SwitchExpr">SwitchExpr</a>, <a href="#doc-xpath40-TypeswitchExpr">TypeswitchExpr</a>, </span></span><a href="#doc-xpath40-IfExpr">IfExpr</a>, <span class="xquery"><span class="xquery"><a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a>, </span></span> and <a href="#doc-xpath40-PipelineExpr">PipelineExpr</a>. Each of these expressions is described in a separate section of this document.</span><span class="modify_version">After the comma, the expressions that have next lowest precedence are <span class="xquery"><span class="xquery"><a href="#doc-xpath40-FLWORExpr">FLWORExpr</a>,</span></span><span class="xpath"><span class="xpath"><a href="#doc-xpath40-ForExpr">ForExpr</a>, <a href="#doc-xpath40-LetExpr">LetExpr</a>, </span></span><a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a>, <span class="xquery"><span class="xquery"><a href="#doc-xpath40-SwitchExpr">SwitchExpr</a>, <a href="#doc-xpath40-TypeswitchExpr">TypeswitchExpr</a>, </span></span><a href="#doc-xpath40-IfExpr">IfExpr</a>, <span class="xquery"><span class="xquery"><a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a>, </span></span> and <a href="#doc-xpath40-OrExpr"><span class="deltaxml-old" style="background:#FF5555">OrExpr</span></a><a href="#doc-xpath40-PipelineExpr"><span class="deltaxml-new" style="background:#90EE90">PipelineExpr</span></a>. Each of these expressions is described in a separate section of this document.</span></p><div class="div2"><h3><a id="comments"></a>4.1 Comments</h3><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-Comment" id="doc-xpath40-Comment"></a>[<span class="deltaxml-old" style="background:#FF5555">282</span><span class="deltaxml-new" style="background:#90EE90">283</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-Comment">Comment</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"(:" (<a href="#doc-xpath40-CommentContents">CommentContents</a> | <a href="#doc-xpath40-Comment">Comment</a>)* ":)"</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>"(:" (<a href="#doc-xpath40-CommentContents">CommentContents</a> | <a href="#doc-xpath40-Comment">Comment</a>)* ":)"</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-comments">gn: comments</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-CommentContents" id="doc-xpath40-CommentContents"></a>[<span class="deltaxml-old" style="background:#FF5555">295</span><span class="deltaxml-new" style="background:#90EE90">296</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-CommentContents">CommentContents</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>(<a href="#prod-xpath40-Char">Char</a>+ - (Char* ('(:' | ':)') Char*))</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>(<a href="#prod-xpath40-Char">Char</a>+ - (Char* ('(:' | ':)') Char*))</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>Comments may be used to provide information relevant to programmers who read <span class="xquery"><span class="xquery">a query, either in the <a title="Prolog" class="termref" href="#dt-prolog">Prolog</a> or in the <a title="query body" class="termref" href="#dt-queryBody">Query Body</a></span></span><span class="xpath"><span class="xpath">an expression</span></span>. Comments are lexical constructs only, and do not affect <span class="xquery"><span class="xquery">query</span></span><span class="xpath"><span class="xpath">expression</span></span> processing.</p><p>Comments are strings, delimited by the symbols <code>(:</code> and <code>:)</code>. Comments may be nested.</p><p>A comment may be used anywhere <a title="ignorable whitespace" class="termref" href="#IgnorableWhitespace">ignorable whitespace</a> is allowed (see <a href="#DefaultWhitespaceHandling"><b>A.3.5.1 Default Whitespace Handling</b></a>).</p><p>The following is an example of a comment:</p><div class="exampleInner"><pre xml:space="preserve">(: Houston, we have a problem :)</pre></div></div><div class="div2"><h3><a id="id-primary-expressions"></a>4.2 Primary Expressions</h3><p> [<a id="dt-primary-expression" title="primary expression">Definition</a>: <b>Primary expressions</b> are the basic primitives of the language. They include literals, variable references, context value references, <span class="xquery"><span class="xquery">constructors, </span></span> and function calls. A primary expression may also be created by enclosing any expression in parentheses, which is sometimes helpful in controlling the precedence of operators.] <span class="xquery"><span class="xquery">Node Constructors are described in <a href="#id-constructors"><b>4.12 Node Constructors</b></a>.</span></span>Map and Array Constructors are described in <a href="#id-maps"><b>4.14.1 Maps</b></a> and <a href="#id-arrays"><b>4.14.2 Arrays</b></a>. <span class="xquery"><span class="xquery">String Constructors are described in <a href="#id-string-constructors"><b>4.9.3 String Constructors</b></a>.</span></span></p><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-PrimaryExpr" id="doc-xpath40-PrimaryExpr"></a>[<span class="deltaxml-old" style="background:#FF5555">170</span><span class="deltaxml-new" style="background:#90EE90">171</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-PrimaryExpr">PrimaryExpr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-Literal">Literal</a><br>| <a href="#doc-xpath40-VarRef">VarRef</a><br>| <a href="#doc-xpath40-ParenthesizedExpr">ParenthesizedExpr</a><br>| <a href="#doc-xpath40-ContextValueRef">ContextValueRef</a><br>| <a href="#doc-xpath40-FunctionCall">FunctionCall</a><br>| <a href="#doc-xpath40-OrderedExpr">OrderedExpr</a><br>| <a href="#doc-xpath40-UnorderedExpr">UnorderedExpr</a><br>| <a href="#doc-xpath40-NodeConstructor">NodeConstructor</a><br>| <a href="#doc-xpath40-FunctionItemExpr">FunctionItemExpr</a><br>| <a href="#doc-xpath40-MapConstructor">MapConstructor</a><br>| <a href="#doc-xpath40-ArrayConstructor">ArrayConstructor</a><br>| <a href="#doc-xpath40-StringTemplate">StringTemplate</a><br>| <a href="#doc-xpath40-StringConstructor">StringConstructor</a><br>| <a href="#doc-xpath40-UnaryLookup">UnaryLookup</a></code></td></tr><tr><td><code><a href="#doc-xpath40-Literal">Literal</a><br>| <a href="#doc-xpath40-VarRef">VarRef</a><br>| <a href="#doc-xpath40-ParenthesizedExpr">ParenthesizedExpr</a><br>| <a href="#doc-xpath40-ContextValueRef">ContextValueRef</a><br>| <a href="#doc-xpath40-FunctionCall">FunctionCall</a><br>| <a href="#doc-xpath40-OrderedExpr">OrderedExpr</a><br>| <a href="#doc-xpath40-UnorderedExpr">UnorderedExpr</a><br>| <a href="#doc-xpath40-NodeConstructor">NodeConstructor</a><br>| <a href="#doc-xpath40-FunctionItemExpr">FunctionItemExpr</a><br>| <a href="#doc-xpath40-MapConstructor">MapConstructor</a><br>| <a href="#doc-xpath40-ArrayConstructor">ArrayConstructor</a><br>| <a href="#doc-xpath40-StringTemplate">StringTemplate</a><br>| <a href="#doc-xpath40-StringConstructor">StringConstructor</a><br>| <a href="#doc-xpath40-UnaryLookup">UnaryLookup</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-FunctionItemExpr" id="doc-xpath40-FunctionItemExpr"></a>[<span class="deltaxml-old" style="background:#FF5555">209</span><span class="deltaxml-new" style="background:#90EE90">210</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-FunctionItemExpr">FunctionItemExpr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-NamedFunctionRef">NamedFunctionRef</a> | <a href="#doc-xpath40-InlineFunctionExpr">InlineFunctionExpr</a></code></td></tr><tr><td><code><a href="#doc-xpath40-NamedFunctionRef">NamedFunctionRef</a> | <a href="#doc-xpath40-InlineFunctionExpr">InlineFunctionExpr</a></code></td></tr></tbody></table><div class="div3"><h4><a id="id-literals"></a>4.2.1 Literals</h4><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-Literal" id="doc-xpath40-Literal"></a>[<span class="deltaxml-old" style="background:#FF5555">171</span><span class="deltaxml-new" style="background:#90EE90">172</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-Literal">Literal</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-NumericLiteral">NumericLiteral</a> | <a href="#doc-xpath40-StringLiteral">StringLiteral</a></code></td></tr><tr><td><code><a href="#doc-xpath40-NumericLiteral">NumericLiteral</a> | <a href="#doc-xpath40-StringLiteral">StringLiteral</a></code></td></tr></tbody></table><p> [<a id="dt-literal" title="literal">Definition</a>: A <b>literal</b> is a direct syntactic representation of an atomic item.] XQuery 4.0 and XPath 4.0 supports two kinds of literals: numeric literals and string literals.</p><div class="div4"><h5><a id="id-numeric-literals"></a>4.2.1.1 Numeric Literals</h5><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-filter-expression">⬇</a>&nbsp;<a href="#id-function-coercion">⬆</a></p><ol><li><p> Numeric literals can now be written in hexadecimal or binary notation; and underscores can be included for readability. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/429">429</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/433">433</a>&nbsp;25 April 2023]</i></p></li></ol></div><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-NumericLiteral" id="doc-xpath40-NumericLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">172</span><span class="deltaxml-new" style="background:#90EE90">173</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-NumericLiteral">NumericLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-IntegerLiteral">IntegerLiteral</a> | <a href="#doc-xpath40-HexIntegerLiteral">HexIntegerLiteral</a> | <a href="#doc-xpath40-BinaryIntegerLiteral">BinaryIntegerLiteral</a> | <a href="#doc-xpath40-DecimalLiteral">DecimalLiteral</a> | <a href="#doc-xpath40-DoubleLiteral">DoubleLiteral</a></code></td></tr><tr><td><code><a href="#doc-xpath40-IntegerLiteral">IntegerLiteral</a> | <a href="#doc-xpath40-HexIntegerLiteral">HexIntegerLiteral</a> | <a href="#doc-xpath40-BinaryIntegerLiteral">BinaryIntegerLiteral</a> | <a href="#doc-xpath40-DecimalLiteral">DecimalLiteral</a> | <a href="#doc-xpath40-DoubleLiteral">DoubleLiteral</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-IntegerLiteral" id="doc-xpath40-IntegerLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">266</span><span class="deltaxml-new" style="background:#90EE90">267</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-IntegerLiteral">IntegerLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-Digits">Digits</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code><a href="#doc-xpath40-Digits">Digits</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-HexIntegerLiteral" id="doc-xpath40-HexIntegerLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">267</span><span class="deltaxml-new" style="background:#90EE90">268</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-HexIntegerLiteral">HexIntegerLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"0x" <a href="#doc-xpath40-HexDigits">HexDigits</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>"0x" <a href="#doc-xpath40-HexDigits">HexDigits</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-BinaryIntegerLiteral" id="doc-xpath40-BinaryIntegerLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">268</span><span class="deltaxml-new" style="background:#90EE90">269</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-BinaryIntegerLiteral">BinaryIntegerLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"0b" <a href="#doc-xpath40-BinaryDigits">BinaryDigits</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>"0b" <a href="#doc-xpath40-BinaryDigits">BinaryDigits</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-DecimalLiteral" id="doc-xpath40-DecimalLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">269</span><span class="deltaxml-new" style="background:#90EE90">270</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-DecimalLiteral">DecimalLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>("." <a href="#doc-xpath40-Digits">Digits</a>) | (<a href="#doc-xpath40-Digits">Digits</a> "." <a href="#doc-xpath40-Digits">Digits</a>?)</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>("." <a href="#doc-xpath40-Digits">Digits</a>) | (<a href="#doc-xpath40-Digits">Digits</a> "." <a href="#doc-xpath40-Digits">Digits</a>?)</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-DoubleLiteral" id="doc-xpath40-DoubleLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">270</span><span class="deltaxml-new" style="background:#90EE90">271</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-DoubleLiteral">DoubleLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>(("." <a href="#doc-xpath40-Digits">Digits</a>) | (<a href="#doc-xpath40-Digits">Digits</a> ("." <a href="#doc-xpath40-Digits">Digits</a>?)?)) [eE] [+-]? <a href="#doc-xpath40-Digits">Digits</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>(("." <a href="#doc-xpath40-Digits">Digits</a>) | (<a href="#doc-xpath40-Digits">Digits</a> ("." <a href="#doc-xpath40-Digits">Digits</a>?)?)) [eE] [+-]? <a href="#doc-xpath40-Digits">Digits</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-Digits" id="doc-xpath40-Digits"></a>[<span class="deltaxml-old" style="background:#FF5555">289</span><span class="deltaxml-new" style="background:#90EE90">290</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-Digits">Digits</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-DecDigit">DecDigit</a> ((<a href="#doc-xpath40-DecDigit">DecDigit</a> | "_")* <a href="#doc-xpath40-DecDigit">DecDigit</a>)?</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code><a href="#doc-xpath40-DecDigit">DecDigit</a> ((<a href="#doc-xpath40-DecDigit">DecDigit</a> | "_")* <a href="#doc-xpath40-DecDigit">DecDigit</a>)?</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-DecDigit" id="doc-xpath40-DecDigit"></a>[<span class="deltaxml-old" style="background:#FF5555">290</span><span class="deltaxml-new" style="background:#90EE90">291</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-DecDigit">DecDigit</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>[0-9]</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>[0-9]</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-HexDigits" id="doc-xpath40-HexDigits"></a>[<span class="deltaxml-old" style="background:#FF5555">291</span><span class="deltaxml-new" style="background:#90EE90">292</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-HexDigits">HexDigits</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-HexDigit">HexDigit</a> ((<a href="#doc-xpath40-HexDigit">HexDigit</a> | "_")* <a href="#doc-xpath40-HexDigit">HexDigit</a>)?</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code><a href="#doc-xpath40-HexDigit">HexDigit</a> ((<a href="#doc-xpath40-HexDigit">HexDigit</a> | "_")* <a href="#doc-xpath40-HexDigit">HexDigit</a>)?</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-HexDigit" id="doc-xpath40-HexDigit"></a>[<span class="deltaxml-old" style="background:#FF5555">292</span><span class="deltaxml-new" style="background:#90EE90">293</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-HexDigit">HexDigit</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>[0-9a-fA-F]</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>[0-9a-fA-F]</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-BinaryDigits" id="doc-xpath40-BinaryDigits"></a>[<span class="deltaxml-old" style="background:#FF5555">293</span><span class="deltaxml-new" style="background:#90EE90">294</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-BinaryDigits">BinaryDigits</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-BinaryDigit">BinaryDigit</a> ((<a href="#doc-xpath40-BinaryDigit">BinaryDigit</a> | "_")* <a href="#doc-xpath40-BinaryDigit">BinaryDigit</a>)?</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code><a href="#doc-xpath40-BinaryDigit">BinaryDigit</a> ((<a href="#doc-xpath40-BinaryDigit">BinaryDigit</a> | "_")* <a href="#doc-xpath40-BinaryDigit">BinaryDigit</a>)?</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-BinaryDigit" id="doc-xpath40-BinaryDigit"></a>[<span class="deltaxml-old" style="background:#FF5555">294</span><span class="deltaxml-new" style="background:#90EE90">295</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-BinaryDigit">BinaryDigit</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>[01]</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>[01]</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>The value of a numeric literal is determined as follows (taking the rules in order):</p><ol class="enumar"><li><p>Underscore characters are stripped out. Underscores may be included in a numeric literal to aid readability, but have no effect on the value. For example, <code>1_000_000</code> is equivalent to <code>1000000</code>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Underscores must not appear at the beginning or end of a sequence of digits, only in intermediate positions. Multiple adjacent underscores are allowed.</p></div></li><li><p>A <code>HexIntegerLiteral</code> represents a non-negative integer expressed in hexadecimal: for example <code>0xffff</code> represents the integer 65535, and <code>0xFFFF_FFFF</code> represents the integer 4294967295.</p></li><li><p>A <code>BinaryIntegerLiteral</code> represents a non-negative integer expressed in binary: for example <code>0b101</code> represents the integer 5, and <code>0b1111_1111</code> represents the integer 255.</p></li><li><p>The value of a <b>numeric literal</b> containing no <code>.</code> and no <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:integer</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:integer</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li><li><p>The value of a numeric literal containing <code>.</code> but no <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:decimal</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:decimal</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li><li><p>The value of a numeric literal containing an <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:double</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:double</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li></ol><div class="note"><p class="prefix"><b>Note:</b></p><p>The value of a numeric literal is always non-negative. An expression may appear to include a negative number such as <code>-1</code>, but this is technically an arithmetic expression comprising a unary minus operator followed by a numeric literal.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The effect of the above rules is that in the case of an integer or decimal literal, a dynamic error [<a href="https://qt4cg.org/specifications/xpath-functions-40/#ERRFOAR0002" title="err:FOAR0002">err:FOAR0002</a>]<sup><small>FO40</small></sup> will generally be raised if the literal is outside the range of values supported by the implementation (other options are available: see <a href="https://qt4cg.org/specifications/xpath-functions-40/#op.numeric">Section 4.2 Arithmetic operators on numeric values</a><sup><small>FO</small></sup> for details.)</p><div class="xquery"><p class="xquery">The limits of numeric datatypes are specified in <a href="#id-data-model-conformance"><b>6.3 Data Model Conformance</b></a>.</p></div><div class="xpath"><p class="xpath">The XML Schema specification allows implementations to impose a limit (which must not be less than 18 digits) on the size of integer and decimal values. The full range of values of built-in subtypes of <code>xs:integer</code>, such as <code>xs:long</code> and <code>xs:unsignedLong</code>, can be supported only if the limit is 20 digits or higher. Negative numbers such as the minimum value of <code>xs:long</code> (<code>-9223372036854775808</code>) are technically unary expressions rather than literals, but implementations may prefer to ensure that they are expressible.</p></div></div><p>Here are some examples of numeric literals:</p><ul><li><p><code>12</code> denotes the <code>xs:integer</code> value twelve.</p></li><li><p><code>1_000_000</code> denotes the <code>xs:integer</code> value one million.</p></li><li><p><code>12.5</code> denotes the <code>xs:decimal</code> value twelve and one half.</p></li><li><p><code>3.14159_26535_89793e0</code> is an <code>xs:double</code> value representing the mathematical constant <var>π</var> to 15 decimal places. </p></li><li><p><code>125E2</code> denotes the <code>xs:double</code> value twelve thousand, five hundred.</p></li><li><p><code>0xffff</code> denotes the <code>xs:integer</code> value 65535.</p></li><li><p><code>0b1000_0001</code> denotes the <code>xs:integer</code> value 129.</p></li></ul></div><div class="div4"><h5><a id="id-string-literal"></a>4.2.1.2 String Literals</h5><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-StringLiteral" id="doc-xpath40-StringLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">271</span><span class="deltaxml-new" style="background:#90EE90">272</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-StringLiteral">StringLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-AposStringLiteral">AposStringLiteral</a> | <a href="#doc-xpath40-QuotStringLiteral">QuotStringLiteral</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code><a href="#doc-xpath40-AposStringLiteral">AposStringLiteral</a> | <a href="#doc-xpath40-QuotStringLiteral">QuotStringLiteral</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-AposStringLiteral" id="doc-xpath40-AposStringLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">272</span><span class="deltaxml-new" style="background:#90EE90">273</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-AposStringLiteral">AposStringLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"'" (<a href="#doc-xpath40-PredefinedEntityRef">PredefinedEntityRef</a> | <a href="#doc-xpath40-CharRef">CharRef</a> | <a href="#doc-xpath40-EscapeApos">EscapeApos</a> | [^'&amp;])* "'"</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>"'" (<a href="#doc-xpath40-PredefinedEntityRef">PredefinedEntityRef</a> | <a href="#doc-xpath40-CharRef">CharRef</a> | <a href="#doc-xpath40-EscapeApos">EscapeApos</a> | [^'&amp;])* "'"</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-QuotStringLiteral" id="doc-xpath40-QuotStringLiteral"></a>[<span class="deltaxml-old" style="background:#FF5555">273</span><span class="deltaxml-new" style="background:#90EE90">274</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-QuotStringLiteral">QuotStringLiteral</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>'"' (<a href="#doc-xpath40-PredefinedEntityRef">PredefinedEntityRef</a> | <a href="#doc-xpath40-CharRef">CharRef</a> | <a href="#doc-xpath40-EscapeQuot">EscapeQuot</a> | [^"&amp;])* '"'</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>'"' (<a href="#doc-xpath40-PredefinedEntityRef">PredefinedEntityRef</a> | <a href="#doc-xpath40-CharRef">CharRef</a> | <a href="#doc-xpath40-EscapeQuot">EscapeQuot</a> | [^"&amp;])* '"'</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-PredefinedEntityRef" id="doc-xpath40-PredefinedEntityRef"></a>[<span class="deltaxml-old" style="background:#FF5555">276</span><span class="deltaxml-new" style="background:#90EE90">277</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-PredefinedEntityRef">PredefinedEntityRef</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"&amp;" ("lt" | "gt" | "amp" | "quot" | "apos") ";"</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>"&amp;" ("lt" | "gt" | "amp" | "quot" | "apos") ";"</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-CharRef" id="doc-xpath40-CharRef"></a>[<span class="deltaxml-old" style="background:#FF5555">284</span><span class="deltaxml-new" style="background:#90EE90">285</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-CharRef">CharRef</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="https://www.w3.org/TR/REC-xml/#NT-CharRef">[http://www.w3.org/TR/REC-xml#NT-CharRef]</a><sup><small>XML</small></sup></code></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-xml-version">xgc: xml-version</a> */</td></tr><tr><td><code><a href="https://www.w3.org/TR/REC-xml/#NT-CharRef">[http://www.w3.org/TR/REC-xml#NT-CharRef]</a><sup><small>XML</small></sup></code></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-xml-version">xgc: xml-version</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-xml-version">xgc: xml-version</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-EscapeQuot" id="doc-xpath40-EscapeQuot"></a>[<span class="deltaxml-old" style="background:#FF5555">277</span><span class="deltaxml-new" style="background:#90EE90">278</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-EscapeQuot">EscapeQuot</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>'""'</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>'""'</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-EscapeApos" id="doc-xpath40-EscapeApos"></a>[<span class="deltaxml-old" style="background:#FF5555">278</span><span class="deltaxml-new" style="background:#90EE90">279</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-EscapeApos">EscapeApos</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"''"</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td><code>"''"</code></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>The value of a <b>string literal</b> is an atomic item whose type is <code>xs:string</code> and whose value is the string denoted by the characters between the delimiting apostrophes or quotation marks. If the literal is delimited by apostrophes, two adjacent apostrophes within the literal are interpreted as a single apostrophe. Similarly, if the literal is delimited by quotation marks, two adjacent quotation marks within the literal are interpreted as one quotation mark.</p><div class="xquery"><p class="xquery"> [<a id="dt-predefined-entity-reference" title="predefined entity reference">Definition</a>: A <b>predefined entity reference</b> is a short sequence of characters, beginning with an ampersand, that represents a single character that might otherwise have syntactic significance.] Each predefined entity reference is replaced by the character it represents when the string literal is processed. The predefined entity references recognized by XPath and XQuery are as follows:</p></div><div class="xquery"><div class="medium"><table style="width:60%; border:1px solid" class="medium"><tbody><tr><th style="text-align:center">Entity Reference</th><th style="text-align:center">Character Represented</th></tr><tr><td style="text-align:center"><code>&amp;lt;</code></td><td style="text-align:center"><code>&lt;</code></td></tr><tr><td style="text-align:center"><code>&amp;gt;</code></td><td style="text-align:center"><code>&gt;</code></td></tr><tr><td style="text-align:center"><code>&amp;amp;</code></td><td style="text-align:center"><code>&amp;</code></td></tr><tr><td style="text-align:center"><code>&amp;quot;</code></td><td style="text-align:center"><code>"</code></td></tr><tr><td style="text-align:center"><code>&amp;apos;</code></td><td style="text-align:center"><code>'</code></td></tr></tbody></table></div></div><div class="xquery"><p class="xquery"> [<a id="dt-character-reference" title="character reference">Definition</a>: A <b>character reference</b> is an XML-style reference to a <a href="#Unicode">[Unicode]</a> character, identified by its decimal or hexadecimal codepoint.] For example, the character <span class="unicode-codepoint">U+20AC</span> (<span class="unicode-name">EURO SIGN</span>, <code>€</code>) can be represented by the character reference <code>&amp;#8364;</code> or <code>&amp;#x20ac;</code>. Character references are normatively defined in Section 4.1 of the XML specification (it is <a title="implementation defined" class="termref" href="#dt-implementation-defined">implementation-defined</a> whether the rules in <a href="#XML">[XML 1.0]</a> or <a href="#XML1.1">[XML 1.1]</a> apply.) A <a title="static error" class="termref" href="#dt-static-error">static error</a> [<a href="#ERRXQST0090" title="err:XQST0090">err:XQST0090</a>] is raised if a character reference does not identify a valid character in the version of XML that is in use.</p></div><p>Here are some examples of string literals:</p><ul><li><p><code>"He said, ""I don't like it."""</code> denotes a string containing two quotation marks and one apostrophe.</p></li><li class="xquery"><p><code>"Ben &amp;amp; Jerry&amp;apos;s"</code> denotes the <code>xs:string</code> value <code>"Ben &amp; Jerry's"</code>.</p></li><li class="xquery"><p><code>"&amp;#8364;99.50"</code> denotes the <code>xs:string</code> value <code>"€99.50"</code>.</p></li><li><p>In XQuery, the string literal <code>"&amp;lt;"</code> denotes a string of length 1 containing the single character <code>"&lt;"</code>. In XPath, the string literal <code>"&amp;lt;"</code> denotes a string of length 4 containing the four characters <code>"&amp;"</code>, <code>"l"</code>, <code>"t"</code>, <code>";"</code>. (However, when the XPath expression is embedded in an XML document, the sequence <code>"&amp;lt;"</code> will typically have already been converted to <code>"&lt;"</code> by the XML parser.)</p></li></ul><div class="note"><p class="prefix"><b>Note:</b></p><p>When XPath or XQuery expressions are embedded in contexts where quotation marks have special significance, such as inside XML attributes, or in string literals in a host language such as Java or C#, then additional escaping may be needed.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>Fixed string values can also be written as string templates: see <a href="#id-string-templates"><b>4.9.2 String Templates</b></a>. A string template with no enclosed expressions, such as <code>`Jamaica`</code> evaluates to the same value as the string literals <code>"Jamaica"</code> or <code>'Jamaica'</code>. A string template can contain both single and double quotation marks: <code>`He said: "I don't like it"`</code>. However, there there are some subtle differences:</p><ul><li><p>In string literals, the treatment of character and entity references such as <code>&amp;amp;</code> varies between XQuery and XPath; in string templates, such references are not expanded in either language.</p></li><li><p>String templates can only be used where an expression is expected. String literals are also used in some non-expression contexts, for example in defining an enumeration type: see <a href="#id-enumeration-types"><b>3.2.6 Enumeration Types</b></a>.</p></li><li><p>Curly brackets (<span class="unicode-codepoint">U+007B</span> (<span class="unicode-name">LEFT CURLY BRACKET</span>, <code>{</code>) and <span class="unicode-codepoint">U+007D</span> (<span class="unicode-name">RIGHT CURLY BRACKET</span>, <code>}</code>) ) and backticks (<span class="unicode-codepoint">U+0060</span> (<span class="unicode-name">GRAVE ACCENT, BACKTICK</span>, <code>`</code>) ) have a reserved meaning in string templates.</p></li></ul></div></div><div class="div4"><h5><a id="id-constants-other-types"></a>4.2.1.3 Constants of Other Types</h5><p> The <code>xs:boolean</code> values <code>true</code> and <code>false</code> can be constructed by calls to the <a title="system function" class="termref" href="#dt-system-function">system functions</a><code>fn:true()</code> and <code>fn:false()</code>, respectively. </p><p>Values of other simple types can be constructed by calling the <a title="constructor function" class="termref" href="#dt-constructor-function">constructor function</a> for the given type. The constructor functions for XML Schema built-in types are defined in <a href="https://qt4cg.org/specifications/xpath-functions-40/#constructor-functions-for-xsd-types">Section 20.1 Constructor functions for XML Schema built-in atomic types</a><sup><small>FO</small></sup>. In general, the name of a constructor function for a given type is the same as the name of the type (including its namespace). For example:</p><ul><li><p><code>xs:integer("12")</code> returns the integer value twelve.</p></li><li><p><code>xs:date("2001-08-25")</code> returns an item whose type is <code>xs:date</code> and whose value represents the date 25th August 2001.</p></li><li><p><code>xs:dayTimeDuration("PT5H")</code> returns an item whose type is <code>xs:dayTimeDuration</code> and whose value represents a duration of five hours.</p></li></ul><p>Constructor functions can also be used to create special values that have no literal representation, as in the following examples: </p><ul><li><p><code>xs:float("NaN")</code> returns the special floating-point value, "Not a Number."</p></li><li><p><code>xs:double("INF")</code> returns the special double-precision value, "positive infinity."</p></li></ul><p>Constructor functions are available for all simple types, including union types. For example, if <code>my:dt</code> is a user-defined union type whose member types are <code>xs:date</code>, <code>xs:time</code>, and <code>xs:dateTime</code>, then the expression <code>my:dt("2011-01-10")</code> creates an atomic item of type <code>xs:date</code>. The rules follow XML Schema validation rules for union types: the effect is to choose the first member type that accepts the given string in its lexical space.</p><p>It is also possible to construct values of various types by using a <code>cast</code> expression. For example:</p><ul><li><p><code>9 cast as hatsize</code> returns the atomic item <code>9</code> whose type is <code>hatsize</code>.</p></li></ul></div></div><div class="div3"><h4><a id="id-variables"></a>4.2.2 Variable References</h4><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-VarRef" id="doc-xpath40-VarRef"></a>[<span class="deltaxml-old" style="background:#FF5555">173</span><span class="deltaxml-new" style="background:#90EE90">174</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-VarRef">VarRef</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"$" <a href="#doc-xpath40-EQName">EQName</a></code></td></tr><tr><td><code>"$" <a href="#doc-xpath40-EQName">EQName</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="noid_d4e15028.doc-xpath40-EQName" id="noid_d4e15028.doc-xpath40-EQName"></a>[<span class="deltaxml-old" style="background:#FF5555">265</span><span class="deltaxml-new" style="background:#90EE90">266</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-EQName">EQName</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-QName">QName</a> | <a href="#doc-xpath40-URIQualifiedName">URIQualifiedName</a></code></td></tr><tr><td><code><a href="#doc-xpath40-QName">QName</a> | <a href="#doc-xpath40-URIQualifiedName">URIQualifiedName</a></code></td></tr></tbody></table><p> [<a id="dt-variable-reference" title="variable reference">Definition</a>: A <b>variable reference</b> is an EQName preceded by a $-sign.] An unprefixed variable reference is in no namespace. Two variable references are equivalent if their <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QNames</a> are equal (as defined by the <code>eq</code> operator). The scope of a variable binding is defined separately for each kind of expression that can bind variables.</p><p>Every variable reference must match a name in the <a title="in-scope variables" class="termref" href="#dt-in-scope-variables">in-scope variables</a>. </p><p>Every variable binding has a static scope. The scope defines where references to the variable can validly occur. It is a <a title="static error" class="termref" href="#dt-static-error">static error</a> [<a href="#ERRXPST0008" title="err:XPST0008">err:XPST0008</a>] to reference a variable that is not in scope. If a variable is bound in the <a title="static context" class="termref" href="#dt-static-context">static context</a> for an expression, that variable is in scope for the entire expression except where it is occluded by another binding that uses the same name within that scope.</p><div class="xquery"><p class="xquery">A reference to a variable that was declared <code>external</code>, but was not bound to a value by the external environment, raises a <a title="dynamic error" class="termref" href="#dt-dynamic-error">dynamic error</a> [<a href="#ERRXPDY0002" title="err:XPDY0002">err:XPDY0002</a>].</p></div><p> At evaluation time, the value of a variable reference is the value to which the relevant variable is bound.</p></div><div class="div3"><h4><a id="id-context-value-references"></a>4.2.3 Context Value References</h4><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-ContextValueRef" id="doc-xpath40-ContextValueRef"></a>[<span class="deltaxml-old" style="background:#FF5555">175</span><span class="deltaxml-new" style="background:#90EE90">176</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-ContextValueRef">ContextValueRef</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"."</code></td></tr><tr><td><code>"."</code></td></tr></tbody></table><p>A <b>context value reference</b> evaluates to the <a title="context value" class="termref" href="#dt-context-value">context value</a>.</p><p>In many syntactic contexts, the context value will be a single item. For example this applies on the right-hand side of the <code>/</code> or <code>!</code> operators, or within a <a href="#doc-xpath40-Predicate">Predicate</a>.</p><p>If the <a title="context value" class="termref" href="#dt-context-value">context value</a> is <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#dt-absent">absent</a><sup><small>DM</small></sup>, a context value reference raises a <a title="type error" class="termref" href="#dt-type-error">type error</a> [<a href="#ERRXPDY0002" title="err:XPDY0002">err:XPDY0002</a>].</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Being absent is not the same thing as being empty.</p></div></div><div class="div3"><h4><a id="id-paren-expressions"></a>4.2.4 Parenthesized Expressions</h4><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-ParenthesizedExpr" id="doc-xpath40-ParenthesizedExpr"></a>[<span class="deltaxml-old" style="background:#FF5555">174</span><span class="deltaxml-new" style="background:#90EE90">175</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-ParenthesizedExpr">ParenthesizedExpr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"(" <a href="#doc-xpath40-Expr">Expr</a>? ")"</code></td></tr><tr><td><code>"(" <a href="#doc-xpath40-Expr">Expr</a>? ")"</code></td></tr></tbody></table><p>Parentheses may be used to override the precedence rules. For example, the expression <code>(2 + 4) * 5</code> evaluates to thirty, since the parenthesized expression <code>(2 + 4)</code> is evaluated first and its result is multiplied by five. Without parentheses, the expression <code>2 + 4 * 5</code> evaluates to twenty-two, because the multiplication operator has higher precedence than the addition operator.</p><p>Empty parentheses are used to denote an empty sequence, as described in <a href="#construct_seq"><b>4.7.1 Sequence Concatenation</b></a>.</p></div><div class="div3"><h4><a id="id-enclosed-expr"></a>4.2.5 Enclosed Expressions</h4><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-EnclosedExpr" id="doc-xpath40-EnclosedExpr"></a>[40]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-EnclosedExpr">EnclosedExpr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"{" <a href="#doc-xpath40-Expr">Expr</a>? "}"</code></td></tr><tr><td><code>"{" <a href="#doc-xpath40-Expr">Expr</a>? "}"</code></td></tr></tbody></table><p> [<a id="dt-enclosed-expression" title="enclosed expression">Definition</a>: An <b>enclosed expression</b> is an instance of the <a href="#doc-xpath40-EnclosedExpr">EnclosedExpr</a> production, which allows an optional expression within curly brackets.] [<a id="dt-content-expression" title="content expression">Definition</a>: In an <a title="enclosed expression" class="termref" href="#dt-enclosed-expression">enclosed expression</a>, the optional expression enclosed in curly brackets is called the <b>content expression</b>.] If the <a title="content expression" class="termref" href="#dt-content-expression">content expression</a> is not provided explicitly, the content expression is <code>()</code>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Despite the name, an enclosed expression is not actually an expression in its own right; rather it is a construct that is used in the grammar of many other expressions.</p></div></div></div><div class="div2"><h3><a id="id-postfix-expression"></a>4.3 Postfix Expressions</h3><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-PostfixExpr" id="doc-xpath40-PostfixExpr"></a>[<span class="deltaxml-old" style="background:#FF5555">154</span><span class="deltaxml-new" style="background:#90EE90">155</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-PostfixExpr">PostfixExpr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-PrimaryExpr">PrimaryExpr</a> | <a href="#doc-xpath40-FilterExpr">FilterExpr</a> | <a href="#doc-xpath40-DynamicFunctionCall">DynamicFunctionCall</a> | <a href="#doc-xpath40-LookupExpr">LookupExpr</a> | <a href="#doc-xpath40-FilterExprAM">FilterExprAM</a></code></td></tr><tr><td><code><a href="#doc-xpath40-PrimaryExpr">PrimaryExpr</a> | <a href="#doc-xpath40-FilterExpr">FilterExpr</a> | <a href="#doc-xpath40-DynamicFunctionCall">DynamicFunctionCall</a> | <a href="#doc-xpath40-LookupExpr">LookupExpr</a> | <a href="#doc-xpath40-FilterExprAM">FilterExprAM</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="noid_d4e15160.doc-xpath40-FilterExpr" id="noid_d4e15160.doc-xpath40-FilterExpr"></a>[<span class="deltaxml-old" style="background:#FF5555">153</span><span class="deltaxml-new" style="background:#90EE90">154</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-FilterExpr">FilterExpr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Predicate">Predicate</a></code></td></tr><tr><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Predicate">Predicate</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="noid_d4e15161.doc-xpath40-DynamicFunctionCall" id="noid_d4e15161.doc-xpath40-DynamicFunctionCall"></a>[<span class="deltaxml-old" style="background:#FF5555">155</span><span class="deltaxml-new" style="background:#90EE90">156</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-DynamicFunctionCall">DynamicFunctionCall</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-PositionalArgumentList">PositionalArgumentList</a></code></td></tr><tr><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-PositionalArgumentList">PositionalArgumentList</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="noid_d4e15162.doc-xpath40-LookupExpr" id="noid_d4e15162.doc-xpath40-LookupExpr"></a>[<span class="deltaxml-old" style="background:#FF5555">162</span><span class="deltaxml-new" style="background:#90EE90">163</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-LookupExpr">LookupExpr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Lookup">Lookup</a></code></td></tr><tr><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Lookup">Lookup</a></code></td></tr></tbody></table><p>A postfix expression takes one of the following forms:</p><ul><li><p> [<a id="dt-filter-expression" title="filter expression">Definition</a>: A <b>filter expression</b> is an expression in the form <code>E1[E2]</code>: its effect is to return those items from the value of <code>E1</code> that satisfy the predicate in E2.] </p><p>Filter expressions are described in <a href="#id-filter-expression"><b>4.4 Filter Expressions</b></a>.</p><p>An example of a filter expression is <code>(1 to 100)[. mod 2 = 0]</code> which returns all even numbers in the range 1 to 100.</p><p>The base expression <code>E1</code> can itself be a postfix expression, so multiple predicates are allowed, in the form <code>E1[E2][E3][E4]</code>.</p></li><li><p>An expression (other than a raw EQName) followed by an argument list in parentheses (that is, <code>E1(E2, E3, ...)</code>) is referred to as a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-invocation">dynamic function call</a>. Its effect is to evaluate <code>E1</code> to obtain a function, and then call that function, with <code>E2</code>, <code>E3</code>, <code>...</code> as arguments. Dynamic function calls are described in <a href="#id-dynamic-function-invocation"><b>4.5.2.1 Dynamic Function Calls</b></a>.</p><p>An example of a dynamic function call is <code>$f("a", 2)</code> where the value of variable <code>$f</code> must be a function item.</p></li><li><p>A <code>lookup-expression</code> takes the form <code>E1?K</code>, where <code>E1</code> is an expression returning a sequence of maps or arrays, and <code>K</code> is a key specifier, which indicates which entries in a map, or members in an array, should be selected.</p><p>Lookup expressions are described in <a href="#id-postfix-lookup"><b>4.14.3.1 Postfix Lookup Expressions</b></a>.</p><p>An example of a lookup expression is <code>$emp?name</code>, where the value of variable <code>$emp</code> is a map, and the string <code>"name"</code> is the key of one of the entries in the map.</p></li></ul><p>Postfix expressions are evaluated from left-to-right. For example, the expression <code>$E1[E2]?(E3)(E4)</code> is evaluated by first evaluating the filter expression <code>$E1[E2]</code> to produce a sequence of maps and arrays (say <code>$S</code>), then evaluating the lookup expression <code>$S?(E3)</code> to produce a function item (say <code>$F</code>), then evaluating the dynamic function call <code>$F(E4)</code> to produce the final result.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>The grammar for postfix expressions is defined here in a way designed to link clearly to the semantics of the different kinds of expression. For parsing purposes, the equivalent production rule:</p><div class="exampleInner"><pre xml:space="preserve">PostfixExpr := PrimaryExpr (Predicate | PositionalArgumentList | Lookup)*</pre></div><p>(as used in XPath 3.1) is probably more convenient.</p></div></div><div class="div2"><h3><a id="id-filter-expression"></a>4.4 Filter Expressions</h3><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-function-calls">⬇</a>&nbsp;<a href="#id-numeric-literals">⬆</a></p><ol><li><p> The value of a predicate in a filter expression can now be a sequence of integers. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/816">816</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/996">996</a>&nbsp;6 February 2024]</i></p></li></ol></div><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-FilterExpr" id="doc-xpath40-FilterExpr"></a>[<span class="deltaxml-old" style="background:#FF5555">153</span><span class="deltaxml-new" style="background:#90EE90">154</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-FilterExpr">FilterExpr</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Predicate">Predicate</a></code></td></tr><tr><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Predicate">Predicate</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-Predicate" id="doc-xpath40-Predicate"></a>[<span class="deltaxml-old" style="background:#FF5555">161</span><span class="deltaxml-new" style="background:#90EE90">162</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-Predicate">Predicate</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"[" <a href="#doc-xpath40-Expr">Expr</a> "]"</code></td></tr><tr><td><code>"[" <a href="#doc-xpath40-Expr">Expr</a> "]"</code></td></tr></tbody></table><p>A filter expression consists of a base expression followed by a predicate, which is an expression written in square brackets. The result of the filter expression consists of the items returned by the base expression, filtered by applying the predicate to each item in turn. The ordering of the items returned by a filter expression is the same as their order in the result of the primary expression.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Where the expression before the square brackets is a <a href="#doc-xpath40-ReverseStep">ReverseStep</a> or <a href="#doc-xpath40-ForwardStep">ForwardStep</a>, the expression is technically not a filter expression but an <a href="#doc-xpath40-AxisStep">AxisStep</a>. There are minor differences in the semantics: see <a href="#id-predicate"><b>4.6.5 Predicates within Steps</b></a></p></div><p>Here are some examples of filter expressions:</p><ul><li><p>Given a sequence of products in a variable, return only those products whose price is greater than 100.</p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">$products[price gt 100]</pre></div></div></li><li><p>List all the integers from 1 to 100 that are divisible by 5. (See <a href="#construct_seq"><b>4.7.1 Sequence Concatenation</b></a> for an explanation of the <code>to</code> operator.)</p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">(1 to 100)[. mod 5 eq 0]</pre></div></div></li><li><p>The result of the following expression is the integer 25:</p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">(21 to 29)[5]</pre></div></div></li><li><p>The following example returns the fifth through ninth items in the sequence bound to variable <code>$orders</code>.</p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">$orders[5 to 9]</pre></div></div></li><li><p>The following example illustrates the use of a filter expression as a <a title="step" class="termref" href="#dt-step">step</a> in a <a title="path expression" class="termref" href="#dt-path-expression">path expression</a>. It returns the last chapter or appendix within the book bound to variable <code>$book</code>:</p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">$book/(chapter | appendix)[last()]</pre></div></div></li></ul><p>For each item in the input sequence, the predicate expression is evaluated using an <b>inner focus</b>, defined as follows: The context value is the item currently being tested against the predicate. The context size is the number of items in the input sequence. The context position is the position of the context value within the input sequence. </p><p>For each item in the input sequence, the result of the predicate expression is coerced to an <code>xs:boolean</code> value, called the <a title="predicate truth value" class="termref" href="#dt-predicate-truth-value">predicate truth value</a>, as described below. Those items for which the predicate truth value is <code>true</code> are retained, and those for which the predicate truth value is <code>false</code> are discarded.</p><p> [<a id="dt-predicate-truth-value" title="predicate truth value">Definition</a>: The <b>predicate truth value</b> of a value <code>$V</code> is the result of the expression <code>if ($V instance of xs:numeric+) then ($V = position()) else fn:boolean($V)</code>.] </p><p>Expanding this definition, the predicate truth value can be obtained by applying the following rules, in order:</p><ol class="enumar"><li><p>If the value <var>V</var> of the predicate expression is a sequence whose first item is an instance of the type <code>xs:numeric</code>, then:</p><ol class="enumla"><li><p><var>V</var> must be an instance of the type <code>xs:numeric+</code> (that is, every item in <var>V</var> must be numeric). A type error [<a href="https://qt4cg.org/specifications/xpath-functions-40/#ERRFORG0006" title="err:FORG0006">err:FORG0006</a>]<sup><small>FO40</small></sup> is raised if this is not the case.</p></li><li><p>The predicate truth value is <code>true</code> if <var>V</var> is equal (by the <code>=</code> operator) to the <b>context position</b>, and is <code>false</code> otherwise.</p></li></ol><p>In effect this means that an item in the input sequence is selected if its position in the sequence is equal to one or more of the numeric values in the predicate. For example, the predicate <code>[3 to 5]</code> is true for the third, fourth, and fifth items in the input sequence.</p><p><span class="xquery">[<a id="dt-numeric-predicate" title="numeric predicate">Definition</a>: A predicate whose predicate expression returns a value of type <code>xs:numeric+</code> is called a <b>numeric predicate</b>.]</span></p><div class="note"><p class="prefix"><b>Note:</b></p><p>It is possible, though not generally useful, for the value of a numeric predicate to depend on the focus, and thus to differ for different items in the input sequence. For example, the predicate <code>[xs:integer(@seq)]</code> selects those items in the input sequence whose <code>@seq</code> attribute is numerically equal to their position in the input sequence.</p><p>It is also possible, and again not generally useful, for the value of the predicate to be numeric for some items in the input sequence, and boolean for others. For example, the predicate <code>[@special otherwise last()]</code> is true for an item that either has an <code>@special</code> attribute, or is the last item in the input sequence.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The truth value of a numeric predicate does not depend on the order of the numbers in <var>V</var>. The predicates <code>[ 1, 2, 3 ]</code> and <code>[ 3, 2, 1 ]</code> have exactly the same effect. The items in the result of a filter expression always retain the ordering of the input sequence.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The truth value of a numeric predicate whose value is non-integral or non-positive is always false.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>Beware that using boolean operators (<code>and</code>, <code>or</code>, <code>not()</code>) with numeric values may not have the intended effect. For example the predicate <code>[1 or last()]</code> selects every item in the sequence, because <code>or</code> operates on the <a title="effective boolean value" class="termref" href="#dt-ebv">effective boolean value</a> of its operands. The required effect can be achieved with the predicate <code>[1, last()]</code>.</p></div></li><li><p>Otherwise, the predicate truth value is the <a title="effective boolean value" class="termref" href="#dt-ebv">effective boolean value</a> of the predicate expression.</p></li></ol></div><div class="div2"><h3><a id="id-functions"></a>4.5 Functions</h3><p>Functions in XQuery 4.0 and XPath 4.0 arise in two ways:</p><ul><li><p>A <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> contains information about a family of functions with the same name and a defined arity range. These functions are in most cases known statically (they appear in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a>), but there may be further function definitions that are known only dynamically (appearing in the <a title="dynamically known function definitions" class="termref" href="#dt-dynamically-known-function-definitions">dynamically known function definitions</a>).</p></li><li><p><a title="function item" class="termref" href="#dt-function-item">Function items</a> are XDM items that can be called using a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-call">dynamic function call</a>. They are values that can be bound to variables, passed as arguments, returned as function results, and generally manipulated in the same way as other XDM values.</p></li></ul><p>The functions defined by a statically known <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> can be invoked using a <a title="static function call" class="termref" href="#dt-static-function-call">static function call</a>. <a title="function item" class="termref" href="#dt-function-item">Function items</a> corresponding to these definitions can also be obtained, as dynamic values, by evaluating a <a title="named function reference" class="termref" href="#dt-named-function-ref">named function reference</a>. <a title="function item" class="termref" href="#dt-function-item">Function items</a> can also be obtained using the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-function-lookup"><code>fn:function-lookup</code></a> function: in this case the function name and arity do not need to be known statically, and the function definition need not be present in the <a title="static context" class="termref" href="#dt-static-context">static context</a>, so long as it is in the <a title="dynamic context" class="termref" href="#dt-dynamic-context">dynamic context</a>.</p><p>Static and dynamic function calls are described in the following sections.</p><div class="div3"><h4><a id="id-static-functions"></a>4.5.1 Static Function Calls</h4><p>The <a title="static context" class="termref" href="#dt-static-context">static context</a> for an expression includes a set of <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a>. Every <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context has a name (which is an <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a>) and an <a title="arity range" class="termref" href="#dt-arity-range">arity range</a>, which is a range of permitted arities for calls on that function. Two <a title="function definition" class="termref" href="#dt-function-definition">function definitions</a> having the same name must not have overlapping arity ranges. This means that for a given static function call, it is possible to identify the target function definition in the static context unambiguously from knowledge of the function name and the number of supplied arguments.</p><p>A <a title="static function call" class="termref" href="#dt-static-function-call">static function call</a> is bound to a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context by matching the name and arity. If the function call has <var>P</var> positional arguments followed by <var>K</var> keyword arguments, then the required arity is <var>P+K</var>, and the static context must include a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> whose name matches the <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a> in the function call, and whose <a title="arity range" class="termref" href="#dt-arity-range">arity range</a> includes this required arity. This is the function chosen to be called. The result of the function is obtained by evaluating the expression that forms its implementation, with a dynamic context that provides values for all the declared parameters, initialized as described in <a href="#id-eval-static-function-call"><b>4.5.1.2 Evaluating Static Function Calls</b></a> below.</p><p>Similarly, a function reference of the form <code>f#N</code> binds to a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context whose name matches <var>f</var> where <code>MinP ≤ N and MaxP ≥ N</code>. The result of evaluating a function reference is a <a title="function item" class="termref" href="#dt-function-item">function item</a> which can be called using a dynamic function call. Function items are never variadic and their arguments are always supplied positionally. For example, the function reference <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-concat"><code>fn:concat#3</code></a> returns a function item with arity 3, which is always called by supplying three positional arguments, and whose effect is the same as a static call on <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-concat"><code>fn:concat</code></a> with three positional arguments. </p><p>The detailed rules for evaluating static function calls and function references are defined in subsequent sections.</p><div class="div4"><h5><a id="id-function-calls"></a>4.5.1.1 Static Function Call Syntax</h5><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-inline-func">⬇</a>&nbsp;<a href="#id-filter-expression">⬆</a></p><ol><li><p> Keyword arguments are allowed on static function calls, as well as positional arguments. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/155">155</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/159">159</a>&nbsp;30 September 2020]</i></p></li></ol></div><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-FunctionCall" id="doc-xpath40-FunctionCall"></a>[<span class="deltaxml-old" style="background:#FF5555">178</span><span class="deltaxml-new" style="background:#90EE90">179</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-FunctionCall">FunctionCall</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-EQName">EQName</a><a href="#doc-xpath40-ArgumentList">ArgumentList</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-reserved-function-names">xgc: reserved-function-names</a> */</td></tr><tr><td><code><a href="#doc-xpath40-EQName">EQName</a><a href="#doc-xpath40-ArgumentList">ArgumentList</a></code></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-reserved-function-names">xgc: reserved-function-names</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-reserved-function-names">xgc: reserved-function-names</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-parens">gn: parens</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-ArgumentList" id="doc-xpath40-ArgumentList"></a>[<span class="deltaxml-old" style="background:#FF5555">156</span><span class="deltaxml-new" style="background:#90EE90">157</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-ArgumentList">ArgumentList</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"(" ((<a href="#doc-xpath40-PositionalArguments">PositionalArguments</a> ("," <a href="#prod-xpath40-KeywordArguments">KeywordArguments</a>)?) | <a href="#prod-xpath40-KeywordArguments">KeywordArguments</a>)? ")"</code></td></tr><tr><td><code>"(" ((<a href="#doc-xpath40-PositionalArguments">PositionalArguments</a> ("," <a href="#prod-xpath40-KeywordArguments">KeywordArguments</a>)?) | <a href="#prod-xpath40-KeywordArguments">KeywordArguments</a>)? ")"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="noid_d4e15609.doc-xpath40-PositionalArguments" id="noid_d4e15609.doc-xpath40-PositionalArguments"></a>[<span class="deltaxml-old" style="background:#FF5555">158</span><span class="deltaxml-new" style="background:#90EE90">159</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-PositionalArguments">PositionalArguments</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>(<a href="#doc-xpath40-Argument">Argument</a> ++ ",")</code></td></tr><tr><td><code>(<a href="#doc-xpath40-Argument">Argument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-Argument" id="doc-xpath40-Argument"></a>[<span class="deltaxml-old" style="background:#FF5555">179</span><span class="deltaxml-new" style="background:#90EE90">180</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-Argument">Argument</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-ExprSingle">ExprSingle</a> | <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td></tr><tr><td><code><a href="#doc-xpath40-ExprSingle">ExprSingle</a> | <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-ArgumentPlaceholder" id="doc-xpath40-ArgumentPlaceholder"></a>[<span class="deltaxml-old" style="background:#FF5555">180</span><span class="deltaxml-new" style="background:#90EE90">181</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"?"</code></td></tr><tr><td><code>"?"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="noid_d4e15612.doc-xpath40-KeywordArguments" id="noid_d4e15612.doc-xpath40-KeywordArguments"></a>[<span class="deltaxml-old" style="background:#FF5555">159</span><span class="deltaxml-new" style="background:#90EE90">160</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-KeywordArguments">KeywordArguments</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>(<a href="#doc-xpath40-KeywordArgument">KeywordArgument</a> ++ ",")</code></td></tr><tr><td><code>(<a href="#doc-xpath40-KeywordArgument">KeywordArgument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-KeywordArgument" id="doc-xpath40-KeywordArgument"></a>[<span class="deltaxml-old" style="background:#FF5555">160</span><span class="deltaxml-new" style="background:#90EE90">161</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-KeywordArgument">KeywordArgument</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-EQName">EQName</a> ":=" <a href="#doc-xpath40-Argument">Argument</a></code></td></tr><tr><td><code><a href="#doc-xpath40-EQName">EQName</a> ":=" <a href="#doc-xpath40-Argument">Argument</a></code></td></tr></tbody></table><p> [<a id="dt-static-function-call" title="static function call">Definition</a>: A <b>static function call</b> consists of an EQName followed by a parenthesized list of zero or more arguments.] </p><p>The argument list consists of zero or more positional arguments, followed by zero or more keyword arguments.</p><p> [<a id="dt-arg-expr" title="argument expression">Definition</a>: An argument to a function call is either an <b>argument expression</b> or an <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a> (<code>?</code>); in both cases it may either be supplied positionally, or identified by a name (called a keyword).] </p><p>This section is concerned with static function calls in which none of the arguments are <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholders</a>. Calls using one or more <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholders</a> are covered in the section <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p>If the function name supplied in a static function call is an unprefixed <a title="lexical QName" class="termref" href="#dt-qname">lexical QName</a>, it is expanded using the <a title="default function namespace" class="termref" href="#dt-default-function-namespace">default function namespace</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a>. </p><p> The <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a> used as the function name and the number of arguments used in the static function call (the required arity) must match the name and arity range of a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a><span> using the rules defined in the previous section</span>; if there is no match, a <a title="static error" class="termref" href="#dt-static-error">static error</a> is raised [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>]. </p><p>Evaluation of static function calls is described in <a href="#id-eval-static-function-call"><b>4.5.1.2 Evaluating Static Function Calls</b></a> .</p><p>Since the arguments of a function call are separated by commas, any <a title="argument expression" class="termref" href="#dt-arg-expr">argument expression</a> that contains a top-level <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a> must be enclosed in parentheses. Here are some illustrative examples of static function calls:</p><ul><li><p><code>my:three-argument-function(1, 2, 3)</code> denotes a static function call with three <span>positional</span> arguments. <span>The corresponding function declaration must define at least three parameters, and may define more, provided they are optional.</span></p></li><li><p><code>my:two-argument-function((1, 2), 3)</code> denotes a static function call with two arguments, the first of which is a sequence of two values. <span>The corresponding function declaration must define at least two parameters, and may define more, provided they are optional.</span></p></li><li><p><code>my:two-argument-function(1, ())</code> denotes a static function call with two arguments, the second of which is an empty sequence.</p></li><li><p><code>my:one-argument-function((1, 2, 3))</code> denotes a static function call with one argument that is a sequence of three values. </p></li><li><p><code>my:one-argument-function(( ))</code> denotes a static function call with one argument that is an empty sequence.</p></li><li><p><code>my:zero-argument-function( )</code> denotes a static function call with zero arguments.</p></li><li><p><code>lang(node := $n, language := 'de')</code> is a static function call with two keyword arguments. The corresponding function declaration defines two parameters, a required parameter <code>language</code> and an optional parameter <code>node</code>. This call supplies values for both parameters. It is equivalent to the call <code>fn:lang('de', $n)</code>. Note that the keyword arguments are in a different order from the parameter declarations. </p></li><li><p><code>sort(//employee, key := fn($e) { xs:decimal($e/salary) })</code> is a static function call with one positional argument and one keyword argument. The corresponding function declaration defines three parameters, a required parameter <code>$input</code>, an optional parameter <code>$collation</code>, and an optional parameter <code>$key</code> This call supplies values for the first and third parameters, leaving the second parameter (<code>$collation</code>) to take its default value. The default value of the <code>$collation</code> parameter is given as <code>fn:default-collation()</code>, so the value supplied to the function is the default collation from the dynamic context of the caller. It is equivalent to the call <code>fn:sort(//employee, fn:default-collation(), fn($e) { xs:decimal($e/salary) })</code>. </p></li></ul><p>An <code>EQName</code> in a <code>KeywordArgument</code> is expanded to a QName value; if there is no prefix, then the name is in no namespace (otherwise the prefix is resolved in the usual way). The keywords used in a function call (after expansion to QNames) must be distinct [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>]; [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>].</p></div><div class="div4"><h5><a id="id-eval-static-function-call"></a>4.5.1.2 Evaluating Static Function Calls</h5><p>This section applies to static function calls where none of the arguments is an <code>ArgumentPlaceholder</code>. For function calls involving placeholders, see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p> When a static function call <var>FC</var> is evaluated with respect to a static context <var>SC</var> and a dynamic context <var>DC</var>, the result is obtained as follows: </p><ol class="enumar"><li><p> The <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> to be used is found in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a> of <var>SC</var>. </p><p>The <b>required arity</b> is the total number of arguments in the function call, including both positional and keyword arguments.</p><p> There can be at most one <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a> component of <var>SC</var> whose function name matches the expanded QName in <var>FC</var> and whose <a title="arity range" class="termref" href="#dt-arity-range">arity range</a> includes the arity of <var>FC</var>’s <code>ArgumentList</code>. </p><p>If there is no such <a title="function definition" class="termref" href="#dt-function-definition">function definition</a>, a static error [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>] is raised.</p></li><li><p>Each parameter in the <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> is matched to an argument expression as follows:</p><ol class="enumla"><li><p>If there are <var>N</var> positional arguments in the function call <var>FC</var>, then the corresponding argument expressions are matched pairwise to the first <var>N</var> parameters in the declaration. For this purpose the required parameters and optional parameters in <var>FD</var> are concatenated into a single list, in order.</p></li><li><p>Any keyword arguments in <var>FC</var> are then matched to parameters (whether required or optional) in <var>FD</var> by comparing the keyword used in <var>FC</var> with the paramater name declared in <var>FD</var>. Each keyword must match the name of a declared parameter [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>], and this must be one that has not already been matched to a positional argument. [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>].</p></li><li><p>If any required parameter has not been matched to any argument in <var>FC</var> by applying the above rules, a static error is reported [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>] </p></li><li><p>If any optional parameter has not been matched to any argument in <var>FC</var> by applying the above rules, then the parameter is matched to the default value expression for that parameter in <var>FD</var>.</p></li></ol></li><li><p> Each argument expression established by the above rules is evaluated with respect to DC. The order of argument evaluation is <a title="implementation   dependent" class="termref" href="#dt-implementation-dependent">implementation dependent</a> and it is not required that an argument be evaluated if the function body can be evaluated without evaluating that argument.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>All argument expressions, including default value expressions, are evaluated in the dynamic context of the function call. It is therefore possible to use a default value expression such as <code>.</code>, or <code>/</code>, or <code>fn:current-dateTime()</code>, whose value depends on the dynamic context of the function call.</p></div><p>If the expression used for the default value of a parameter has no dependencies on the dynamic context, then an implementation <span class="verb">may</span> choose to reuse the same value on repeated function calls rather than re-evaluating it on each function call.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>This is relevant, for example, if the expression constructs new nodes.</p></div></li><li><p>The result of evaluating the argument expression is converted to the required type (the declared type associated with the corresponding parameter in the function declaration, defaulting to <code>item()*</code>) by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>.</p><p><span>This applies both to explicitly supplied arguments, and to values obtained by evaluating default value expressions. In both cases a type error will be raised if the value (after coercion) does not match the required type.</span></p></li><li><p>The result of the function call is obtained as follows:</p><ul><li><p><var>FD</var>’s <span>body</span> is invoked in an implementation-dependent way. The processor makes the following information available to that invocation: </p><ul><li><p>The converted argument values;</p></li><li><p>If the function is <a title="context dependent" class="termref" href="#dt-context-dependent">context dependent</a>, the static context <var>SC</var> and dynamic context <var>DC</var> of the function call. </p></li></ul></li><li><p>The result is converted to the required type (the declared return type in the function declaration, defaulting to <code>item()*</code>) by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>.</p><p>The result of applying the coercion rules is either an instance of <var>FD</var>’s return type or a dynamic error. This result is then the result of evaluating <var>FC</var>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>A host language may define alternative rules for processing the result, especially in the case of external functions implemented using a non-XDM type system.</p></div></li><li><p> Errors raised by system functions are defined in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>. </p></li><li class="xquery"><p> Errors raised by external functions are <a title="implementation defined" class="termref" href="#dt-implementation-defined">implementation-defined</a> (see <a href="#id-consistency-constraints"><b>2.3.6 Consistency Constraints</b></a>). </p></li><li class="xpath"><p> Errors raised by host-language-dependent functions are <a title="implementation defined" class="termref" href="#dt-implementation-defined">implementation-defined</a>. </p></li></ul><div class="example"><div class="exampleHeader"><a id="d5e17270"></a>Example: A System Function</div><p>The following function call uses the function <a href="https://qt4cg.org/specifications/xpath-functions-40/#func-base-uri">Section 2.1.5 fn:base-uri</a><sup><small>FO</small></sup>. Use of <code>SC</code> and <code>DC</code> and errors raised by this function are all defined in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>.</p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">base-uri()</pre></div></div></div></li></ol></div></div><div class="div3"><h4><a id="id-dynamic-functions"></a>4.5.2 Function Items</h4><p>A <a title="function item" class="termref" href="#dt-function-item">function item</a> is an XDM value that can be bound to a variable, or manipulated in various ways by XQuery 4.0 and XPath 4.0 expressions. The most significant such expression is a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-call">dynamic function call</a>, which supplies values of arguments and evaluates the function to produce a result.</p><p>The syntax of dynamic function calls is defined in <a href="#id-dynamic-function-invocation"><b>4.5.2.1 Dynamic Function Calls</b></a>.</p><p>A number of constructs can be used to produce a <a title="function item" class="termref" href="#dt-function-item">function item</a>, notably:</p><ul><li><p>A <b>named function reference</b> (see <a href="#id-named-function-ref"><b>4.5.2.4 Named Function References</b></a>) constructs a function item by reference to <a title="function definition" class="termref" href="#dt-function-definition">function definitions</a> in the static context. For example, <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-node-name"><code>fn:node-name#1</code></a> returns a function item whose effect is to call the static <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-node-name"><code>fn:node-name</code></a> function with one argument.</p></li><li><p>An <b>inline function</b> (see <a href="#id-inline-func"><b>4.5.2.5 Inline Function Expressions</b></a> ) constructs a function item whose <span>body</span> is defined locally. For example, the construct <code>fn($x) { $x + 1 }</code> returns a function item whose effect is to increment the value of the supplied argument.</p></li><li><p>A <b>partial function application</b> (see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>) derives one function item from another by supplying the values of some of its arguments. For example, <code>fn:ends-with(?, ".txt")</code> returns a function item with one argument that tests whether the supplied string ends with the substring <code>".txt"</code>.</p></li><li><p>Maps and arrays are also function items. See <a href="#id-map-constructors"><b>4.14.1.1 Map Constructors</b></a> and <a href="#id-array-constructors"><b>4.14.2.1 Array Constructors</b></a>.</p></li><li><p>The <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-function-lookup"><code>fn:function-lookup</code></a> function can be called to discover functions that are present in the <a title="dynamic context" class="termref" href="#dt-dynamic-context">dynamic context</a>.</p></li><li><p>The <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-load-xquery-module"><code>fn:load-xquery-module</code></a> function can be called to load functions dynamically from an external XQuery library module.</p></li><li><p>Some system functions such as <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-random-number-generator"><code>fn:random-number-generator</code></a> and <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-op"><code>fn:op</code></a> return a <a title="function item" class="termref" href="#dt-function-item">function item</a> as their result.</p></li></ul><p>These constructs are described in detail in the following sections, or in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>.</p><div class="div4"><h5><a id="id-dynamic-function-invocation"></a>4.5.2.1 Dynamic Function Calls</h5><table class="scrap"><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-DynamicFunctionCall" id="doc-xpath40-DynamicFunctionCall"></a>[<span class="deltaxml-old" style="background:#FF5555">155</span><span class="deltaxml-new" style="background:#90EE90">156</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-DynamicFunctionCall">DynamicFunctionCall</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-PositionalArgumentList">PositionalArgumentList</a></code></td></tr><tr><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-PositionalArgumentList">PositionalArgumentList</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-PositionalArgumentList" id="doc-xpath40-PositionalArgumentList"></a>[<span class="deltaxml-old" style="background:#FF5555">157</span><span class="deltaxml-new" style="background:#90EE90">158</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-PositionalArgumentList">PositionalArgumentList</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"(" <a href="#doc-xpath40-PositionalArguments">PositionalArguments</a>? ")"</code></td></tr><tr><td><code>"(" <a href="#doc-xpath40-PositionalArguments">PositionalArguments</a>? ")"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-PositionalArguments" id="doc-xpath40-PositionalArguments"></a>[<span class="deltaxml-old" style="background:#FF5555">158</span><span class="deltaxml-new" style="background:#90EE90">159</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-PositionalArguments">PositionalArguments</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>(<a href="#doc-xpath40-Argument">Argument</a> ++ ",")</code></td></tr><tr><td><code>(<a href="#doc-xpath40-Argument">Argument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="noid_d4e16127.doc-xpath40-Argument" id="noid_d4e16127.doc-xpath40-Argument"></a>[<span class="deltaxml-old" style="background:#FF5555">179</span><span class="deltaxml-new" style="background:#90EE90">180</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-Argument">Argument</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code><a href="#doc-xpath40-ExprSingle">ExprSingle</a> | <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td></tr><tr><td><code><a href="#doc-xpath40-ExprSingle">ExprSingle</a> | <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"></tr><tr style="vertical-align:baseline;"><td><a name="noid_d4e16128.doc-xpath40-ArgumentPlaceholder" id="noid_d4e16128.doc-xpath40-ArgumentPlaceholder"></a>[<span class="deltaxml-old" style="background:#FF5555">180</span><span class="deltaxml-new" style="background:#90EE90">181</span>]&nbsp;&nbsp;&nbsp;</td><td><code><a href="#prod-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td><td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td><td><code>"?"</code></td></tr><tr><td><code>"?"</code></td></tr></tbody></table><p> [<a id="dt-dynamic-function-invocation" title="dynamic function call">Definition</a>: A <b>dynamic function call</b> consists of a base expression that returns the function and a parenthesized list of zero or more arguments (<a title="argument expression" class="termref" href="#dt-arg-expr">argument expressions</a> or ArgumentPlaceholders).] </p><p> A dynamic function call is evaluated as described in <a href="#id-eval-dynamic-function-call"><b>4.5.2.2 Evaluating Dynamic Function Calls</b></a>. </p><p>The following are examples of some dynamic function calls:</p><ul><li><p>This example calls the function contained in <code>$f</code>, passing the arguments 2 and 3: </p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">$f(2, 3)</pre></div></div></li><li><p>This example fetches the second item from sequence <code>$f</code>, treats it as a function and calls it, passing an <code>xs:string</code> argument: </p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">$f[2]("Hi there")</pre></div></div></li><li><p>This example calls the function <code>$f</code> passing no arguments, and filters the result with a positional predicate: </p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">$f()[2]</pre></div></div></li></ul><div class="note"><p class="prefix"><b>Note:</b></p><p>Arguments in a dynamic function call are always supplied positionally.</p></div></div><div class="div4"><h5><a id="id-eval-dynamic-function-call"></a>4.5.2.2 Evaluating Dynamic Function Calls</h5><p>This section applies to dynamic function calls whose arguments do not include an <code>ArgumentPlaceholder</code>. For function calls that include a placeholder, see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p> [<a id="dt-dynamic-function-call" title="dynamic function call">Definition</a>: A <b>dynamic function call</b> is an expression that is evaluated by calling a <a title="function item" class="termref" href="#dt-function-item">function item</a>, which is typically obtained dynamically.] </p><p> When a dynamic function call <var>FC</var> is evaluated, the result is obtained as follows: </p><ol class="enumar"><li><p> The <a title="function item" class="termref" href="#dt-function-item">function item</a><var>FI</var> to be called is obtained by evaluating the base expression of the function call. If this yields a sequence consisting of a single function item whose arity matches the number of arguments in the <code>ArgumentList</code>, let <var>FI</var> denote that function item. Otherwise, a type error is raised [<a href="#ERRXPTY0004" title="err:XPTY0004">err:XPTY0004</a>]. </p><div class="note"><p class="prefix"><b>Note:</b></p><p>Keyword arguments are not allowed in a dynamic function call.</p></div></li><li><p><a title="argument expression" class="termref" href="#dt-arg-expr">Argument expressions</a> are evaluated, producing <b>argument values</b>. The order of argument evaluation is <a title="implementation   dependent" class="termref" href="#dt-implementation-dependent">implementation-dependent</a> and an argument need not be evaluated if the function body can be evaluated without evaluating that argument.</p></li><li><p> Each argument value is converted to the corresponding parameter type in <var>FI</var>’s signature by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>, resulting in a <b>converted argument value</b></p></li><li><p>If <var>FI</var> is a map, it is evaluated as described in <a href="#id-map-lookup"><b>4.14.1.2 Maps as Functions</b></a>.</p></li><li><p>If <var>FI</var> is an array, it is evaluated as described in <a href="#id-array-lookup"><b>4.14.2.2 Arrays as Functions</b></a>.</p></li><li><p> If <var>FI</var>’s <span>body</span> is an XQuery 4.0 and XPath 4.0 expression (for example, if <var>FI</var> is <span class="xquery"><span class="xquery">a <a title="user-defined function" class="termref" href="#dt-udf">user-defined function</a> or</span></span> an <a title="anonymous function" class="termref" href="#dt-anonymous-function">anonymous function</a>, or a <a title="partially applied function" class="termref" href="#dt-partially-applied-function">partial application</a> of such a function): </p><ol class="enumla"><li><p><var>FI</var>’s <span>body</span> is evaluated. The static context for this evaluation is the static context of the XQuery 4.0 and XPath 4.0 expression. The dynamic context for this evaluation is obtained by taking the dynamic context of the <span class="xquery"><span class="xquery">module</span></span><span class="xpath"><span class="xpath"><code>InlineFunctionExpr</code></span></span> that contains the <code>FunctionBody</code>, and making the following changes: </p><ul><li><p> The <a title="focus" class="termref" href="#dt-focus">focus</a> (context value, context position, and context size) is <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#dt-absent">absent</a><sup><small>DM</small></sup>. </p></li><li><p> In the <a title="variable values" class="termref" href="#dt-variable-values">variable values</a> component of the dynamic context, each converted argument value is bound to the corresponding parameter name. </p><p><span>When this is done, the converted argument values retain their <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic types</a>, even where these are <a title="subtype" class="termref" href="#dt-subtype">subtypes</a> of the declared parameter types.</span> For example, a function with a parameter <code>$p</code> of type <code>xs:decimal</code> can be called with an argument of type <code>xs:integer</code>, which is derived from <code>xs:decimal</code>. During the processing of this function call, the value of <code>$p</code> inside the body of the function retains its <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic type</a> of <code>xs:integer</code>. </p></li><li><p><var>FI</var>’s nonlocal variable bindings are also added to the <a title="variable values" class="termref" href="#dt-variable-values">variable values</a>. (Note that the names of the nonlocal variables are by definition disjoint from the parameter names, so there can be no conflict.) </p></li></ul></li><li><p> The value returned by evaluating the function body is then converted to the declared return type of <var>FI</var> by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>. The result is then the result of evaluating <var>FC</var>. </p><p> As with argument values, the value returned by a function retains its <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic type</a>, which may be a <a title="subtype" class="termref" href="#dt-subtype">subtype</a> of the declared return type of <var>FI</var>. For example, a function that has a declared return type of <code>xs:decimal</code> may in fact return a value of dynamic type <code>xs:integer</code>. </p></li></ol><div class="example"><div class="exampleHeader"><a id="d5e17663"></a>Example: Derived Types and Nonlocal Variable Bindings</div><p><code>$incr</code> is a nonlocal variable that is available within the function because its variable binding has been added to the variable values of the function.. Even though the parameter and return type of this function are both <code>xs:decimal</code>, the more specific type <code>xs:integer</code> is preserved in both cases.</p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">let $incr := 1
 let $f := function($i as xs:decimal) as xs:decimal { $i + $incr }
 return $f(5)</pre></div></div></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="d5e17678"></a>Example: Using the Context Value in an Anonymous Function</div><p>The following example will raise a <a title="type error" class="termref" href="#dt-type-error">type error</a> [<a href="#ERRXPDY0002" title="err:XPDY0002">err:XPDY0002</a>]:</p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">let $vat := function() { @vat + @price }
 return doc('wares.xml')/shop/article/$vat()</pre></div></div><p>Instead, the context value can be used as an argument to the anonymous function:</p><div class="parse-test"><div class="exampleInner"><pre xml:space="preserve">let $vat := function($art) { $art/@vat + $art/@price }
diff --git a/pr/1686/xquery-40/shared-40-diff.html b/pr/1686/xquery-40/shared-40-diff.html
index be4ca06c2..1039154df 100644
--- a/pr/1686/xquery-40/shared-40-diff.html
+++ b/pr/1686/xquery-40/shared-40-diff.html
@@ -10059,7 +10059,7 @@ <h2><a id="id-expressions"></a>4 Expressions</h2>
             <a href="#doc-xpath40-IfExpr">IfExpr</a>,
 <span class="xquery"><span class="xquery">
                <a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a>, </span></span>
-and <a href="#doc-xpath40-OrExpr">OrExpr</a>. Each of these expressions is described in a separate section of this document.</p>
+and <a href="#doc-xpath40-PipelineExpr">PipelineExpr</a>. Each of these expressions is described in a separate section of this document.</p>
             <div class="div2">
                
                <h3><a id="comments"></a>4.1 Comments</h3>
diff --git a/pr/1686/xquery-40/shared-40.html b/pr/1686/xquery-40/shared-40.html
index 4515b3f51..930c2f93d 100644
--- a/pr/1686/xquery-40/shared-40.html
+++ b/pr/1686/xquery-40/shared-40.html
@@ -9820,7 +9820,7 @@ <h2><a id="id-expressions"></a>4 Expressions</h2>
             <a href="#doc-xpath40-IfExpr">IfExpr</a>,
 <span class="xquery"><span class="xquery">
                <a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a>, </span></span>
-and <a href="#doc-xpath40-OrExpr">OrExpr</a>. Each of these expressions is described in a separate section of this document.</p>
+and <a href="#doc-xpath40-PipelineExpr">PipelineExpr</a>. Each of these expressions is described in a separate section of this document.</p>
             <div class="div2">
                
                <h3><a id="comments"></a>4.1 Comments</h3>
diff --git a/pr/1686/xquery-40/shared-40.xml b/pr/1686/xquery-40/shared-40.xml
index 670de2a54..0ca0e956a 100644
--- a/pr/1686/xquery-40/shared-40.xml
+++ b/pr/1686/xquery-40/shared-40.xml
@@ -4483,7 +4483,7 @@ return $f(12.3)</pre></div></div><div class="xquery"><p class="xquery">With XQue
             <a href="#doc-xpath40-IfExpr">IfExpr</a>,
 <span class="xquery"><span class="xquery">
                <a href="#doc-xpath40-TryCatchExpr">TryCatchExpr</a>, </span></span>
-and <a href="#doc-xpath40-OrExpr">OrExpr</a>. Each of these expressions is described in a separate section of this document.</p><div class="div2">
+and <a href="#doc-xpath40-PipelineExpr">PipelineExpr</a>. Each of these expressions is described in a separate section of this document.</p><div class="div2">
 <h3><a id="comments"/>4.1 Comments</h3><table class="scrap"><tbody><tr style="vertical-align:baseline;"><tr style="vertical-align:baseline;"><td><a name="doc-xpath40-Comment" id="doc-xpath40-Comment"/>[283]   </td><td><code><a href="#prod-xpath40-Comment">Comment</a></code></td><td>   ::=   </td><td><code>"(:"  (<a href="#doc-xpath40-CommentContents">CommentContents</a>  |  <a href="#doc-xpath40-Comment">Comment</a>)*  ":)"</code></td><td style="text-align: right;" class="prodComment">/* 
                      <a href="#ws-explicit">ws: explicit</a>
                    */</td></tr><td><code>"(:"  (<a href="#doc-xpath40-CommentContents">CommentContents</a>  |  <a href="#doc-xpath40-Comment">Comment</a>)*  ":)"</code></td><td style="text-align: right;" class="prodComment">/* 
diff --git a/pr/1686/xquery-40/xpath-40-autodiff.html b/pr/1686/xquery-40/xpath-40-autodiff.html
index 987e3db00..8adb0f440 100644
--- a/pr/1686/xquery-40/xpath-40-autodiff.html
+++ b/pr/1686/xquery-40/xpath-40-autodiff.html
@@ -88,7 +88,7 @@
 };
 
 let $f := function($a) { $a mod 2 = 0 }
-return local:filter(1 to 10, $f)</pre></div><p>Here the supplied function <code>$f</code> is an instance of the required type, because its signature defaults the argument type to <code>item()*</code>, which is a supertype of <code>xs:string</code>. The expression <code>$s[$p(.)]</code> could in principle succeed. However, function coercion ensures that the supplied function is wrapped in a function that requires the argument to be of type <code>xs:string</code>, so the call fails with a type error when the wrapping function is invoked supplying an <code>xs:integer</code> as the argument.</p></div></div><div class="div3"><h4><a id="id-coercion-examples"></a>3.4.5 Examples of Coercions</h4><p>This section illustrates the effect of the coercion rules with examples.</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-string"></a>Example: Coercion to <code>xs:string</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:string</code>. For example, the second argument of <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-matches"><code>fn:matches</code></a>, which expects a regular expression. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>"[0-9]"</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>default-language()</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of <code>xs:language</code>, which is a subtype of the required type <code>xs:string</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;[0-9]&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. Unless it has been schema-validated, the typed value will be an instance of <code>xs:untypedAtomic</code>, which is accepted when the required type is <code>xs:string</code>.</p><p>Supplying an element whose type annotation is (say) <code>xs:date</code> will fail with a type error.</p><p class="xpath">The effect is subtly different if XPath 1.0 compatibility mode is enabled. In this case coercion takes the string value of the element node. This differs from the typed value only in the case where the element has been schema-validated and has a type annotation other than <code>xs:string</code>.</p></td></tr><tr><td style="vertical-align:top"><code>xs:anyURI("urn:dummy")</code></td><td style="vertical-align:top"><p>Supplying an instance of <code>xs:anyURI</code> where the expected type is <code>xs:string</code> is permitted; this is one of the pairs of types where implicit casting is allowed.</p></td></tr><tr class="xpath"><td style="vertical-align:top"><code>17.2</code></td><td style="vertical-align:top"><p>Supplying a number where a string is expected raises a type error.</p><p class="xpath">However, if XPath 1.0 compatibility mode is enabled, the number is converted to a string as if by the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-string"><code>fn:string</code></a> function.</p></td></tr><tr class="xpath"><td style="vertical-align:top"><code>//author/@id</code></td><td style="vertical-align:top"><p>Supplying a sequence of nodes where a single string is expected will raise a type error unless either there is only one node in the sequence. In this case the typed value of the node will be used (this must be of type <code>xs:string</code>, <code>xs:untypedAtomic</code>, or <code>xs:anyURI</code>).</p><p class="xpath">If XPath 1.0 compatibility mode is enabled, however, all strings after the first are discarded, and the string value of the first node is used; if the sequence is empty, a zero-length string is supplied.</p></td></tr><tr class="xpath"><td style="vertical-align:top"><code>("red", "green", "blue")</code></td><td style="vertical-align:top"><p>Supplying a sequence of strings where a single string is expected raises a type error.</p><p class="xpath">If XPath 1.0 compatibility mode is enabled, however, all strings after the first are discarded; the effect is as if the supplied value were <code>"red"</code>.</p></td></tr><tr class="xpath"><td style="vertical-align:top"><code>()</code></td><td style="vertical-align:top"><p>Supplying an empty sequence where a single string is expected will fail.</p><p class="xpath">If XPath 1.0 compatibility mode is enabled, however, the value is coerced by applying the function <code>fn:string(())</code>, which delivers the zero-length string.</p></td></tr><tr><td style="vertical-align:top"><code>["a|b"]</code></td><td style="vertical-align:top"><p>Supplying an array holding a single string succeeds, because the rules cause the array to be atomized, and the value after atomization is a single string.</p><p>Supplying an array holding multiple strings would fail.</p><p class="xpath">In XPath 1.0 compatibility mode, supplying an array will fail, regardless of the array contents, because the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-string"><code>fn:string</code></a> function does not accept arrays.</p></td></tr></tbody></table></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-decimal"></a>Example: Coercion to <code>xs:decimal?</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:decimal?</code>. For example, the first argument of <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-seconds"><code>fn:seconds</code></a>, which expects a decimal number of seconds. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>12.4</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>()</code></td><td style="vertical-align:top"><p>None; an empty sequence is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>42</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of <code>xs:integer</code>, which is a subtype of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>math:pi()</code></td><td style="vertical-align:top"><p>The supplied value is an instance of <code>xs:double</code>, which can be converted to <code>xs:decimal</code> under the coercion rules.</p></td></tr><tr><td style="vertical-align:top"><code>("a", "b")[.="c"]</code></td><td style="vertical-align:top"><p>The supplied value is an empty sequence, which is a valid instance of the required type <code>xs:decimal?</code>. However, the processor may (optionally) reject this as an implausible coercion, on the grounds that it can only succeed in one special case, namely where the filter expression selects no values. </p></td></tr><tr><td style="vertical-align:top"><code>(1.5, 2.5, 3.5)</code></td><td style="vertical-align:top"><p>A type error is raised<span class="xpath">, except in the case where XPath 1.0 compatibility is enabled, in which case all values after the first are discarded</span>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;3.14159&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The element node is atomized; unless it has been schema-validated, the result will be <code>"3.14159"</code> as an instance of <code>xs:untypedAtomic</code>. This is converted to an instance of <code>xs:decimal</code> following the rules of the <code>cast as</code> operator.</p></td></tr><tr class="xpath"><td style="vertical-align:top"><code>"12.2"</code></td><td style="vertical-align:top"><p>Supplying a string where an <code>xs:decimal</code> is a type error<span class="xpath">, even if XPath 1.0 compatibility mode is enabled. The rules for compatibility mode would allow conversion if the required type were <code>xs:double</code>, but not for <code>xs:decimal</code></span>. </p></td></tr><tr><td style="vertical-align:top"><code>[1.5]</code></td><td style="vertical-align:top"><p>The array is atomized, and the result is a valid instance of the required type <code>xs:decimal?</code></p></td></tr><tr><td style="vertical-align:top"><code>[]</code></td><td style="vertical-align:top"><p>The array is atomized, and the result is an empty sequence, which is a valid instance of the required type <code>xs:decimal?</code></p></td></tr></tbody></table></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-positive-integer"></a>Example: Coercion to <code>xs:positive-integer</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:positive-integer</code>. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>12</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:integer</code>. Because the supplied value and the required type, <code>xs:positiveInteger</code>, both come under the primitive type <code>xs:decimal</code>, and the value <code>12</code> is within the value space of <code>xs:positiveInteger</code>, the value is relabeled as an <code>xs:positiveInteger</code> and the call succeeds.</p></td></tr><tr><td style="vertical-align:top"><code>12.1</code></td><td style="vertical-align:top"><p>This fails with a type error, because the <code>xs:decimal</code> value <code>12.1</code> is not a value in the value space of <code>xs:positiveInteger</code>. This is so even though casting to <code>xs:positiveInteger</code> would succeed.</p></td></tr><tr><td style="vertical-align:top"><code>math:pi()</code></td><td style="vertical-align:top"><p>This fails with a type error. A value of type <code>xs:double</code> is accepted where the required type is <code>xs:decimal</code> or <code>xs:float</code>, but not where it is <code>xs:positiveInteger</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;1200&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. If the element has not been schema-validated, the result will be an <code>xs:untypedAtomic</code> item, which is successfully cast to the required type <code>xs:positiveInteger</code>. If the element has been validated against a schema, then coercion succeeds if the typed value would itself be acceptable, for example if it is an <code>xs:positiveInteger</code>, or some other <code>xs:decimal</code> within the value space of <code>xs:positiveInteger</code>.</p></td></tr></tbody></table></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-union"></a>Example: Coercion to a union type</div><p>Consider the first parameter of the function <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a>, whose declared type is <code>(xs:string | xs:positiveInteger)</code>. The rules are the same as if it were a union typed declared in an imported schema.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>"amp"</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:string</code>, which is one of the allowed types. The call therefore succeeds.</p></td></tr><tr><td style="vertical-align:top"><code>"#"</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:string</code>, which is one of the allowed types. As far as the coercion rules are concerned, the call therefore succeeds. Under the semantic rules for the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a> function, however, this value is not accepted; a dynamic error (as distinct from a type error) is therefore raised.</p></td></tr><tr><td style="vertical-align:top"><code>0x25</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:integer</code>. Although this is not one of the allowed types, it is acceptable because coercion of the value to type <code>xs:positiveInteger</code> succeeds. The value is relabeled as an instance of <code>xs:positiveInteger</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;0x25&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. Assuming that the node has not been schema-validated, the result is an instance of <code>xs:untypedAtomic</code>. The member types of the choice are tested in order. Conversion to <code>xs:string</code> with the value "0x25" succeeds, so the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a> function is called supplying this string; but the function rejects this string as semantically invalid. The same would happen if the value were, say, &lt;a&gt;37&lt;/a&gt;. Supplying such a value requires an explicit cast, for example <code>fn:char( xs:positiveInteger( ./a ))</code>.</p></td></tr></tbody></table></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-choice"></a>Example: Coercion to a choice type</div><p>Suppose the required type is <code>(record(x as xs:decimal, y as xs:decimal, *) | record(size as enum("S", "M", "L", "XL"), *))</code>.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>{ "x": 1, "y": 2, "z": 3 }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of the first record type: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "size": "M" }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of the second record type: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1, "y": 2, "size": "XL" }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of both record types: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1e0, "y": 2e0, "size": "XL" }</code></td><td style="vertical-align:top"><p>The supplied value is not an instance of the first record type because the fields are of type <code>xs:double</code> rather than <code>xs:decimal</code>. It is however an instance of the second record type. It is therefore accepted <em>as is</em>; the fields <code>x</code> and <code>y</code> are not converted from <code>xs:double</code> to <code>xs:decimal</code>.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1e0, "y": 2e0, "size": "XXL" }</code></td><td style="vertical-align:top"><p>The supplied value is not an instance of the first record type because the fields are of type <code>xs:double</code> rather than <code>xs:decimal</code>, and it is not an instance of the second record type because the <code>size</code> value does not match the enumeration type. Coercion is therefore attempted to the first record type, and succeeds. The <code>x</code> and <code>y</code> fields are coerced to <code>xs:decimal</code>, and the <code>size</code> field is accepted <em>as is</em>.</p></td></tr></tbody></table></div></div></div><div class="div2"><h3><a id="id-predefined-types"></a>3.5 Schema Types</h3><p> [<a id="dt-schema-type" title="schema type">Definition</a>: A <b>schema type</b> is a complex type or simple type as defined in the <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> specifications, including built-in types as well as user-defined types.] </p><p>Every schema type is either a <b>complex type</b> or a <b>simple type</b>; simple types are further subdivided into <b>list types</b>, <b>union types</b>, and <b>atomic types</b> (see <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> for definitions and explanations of these terms.)</p><p>A schema type can appear as a type annotation on an element or attribute node. The type annotation on an element node can be a complex type or a simple type; the type annotation on an attribute node is always a simple type. Non-instantiable types such as <code>xs:NOTATION</code> or <code>xs:anyAtomicType</code> never appear as type annotations, but their derived types can be so used. Union types never appear as type annotations; when an element or attribute is validated against a union type, the resulting type annotation will be one of the types in the transitive membership of the union type.</p><p> [<a id="dt-atomic-type" title="atomic type">Definition</a>: An <b>atomic type</b> is a simple <a title="schema type" class="termref" href="#dt-schema-type">schema type</a> whose <a href="https://www.w3.org/TR/xmlschema11-1/#std-variety">{variety}<sup><small>XS11-1</small></sup></a> is <code>atomic</code>.] </p><p>An <b>atomic type</b> is either a built-in atomic type (defined either in the XSD specification or in this specification), or it is a user-defined atomic type included in an imported schema.</p><p class="xpath">The <a title="in-scope schema type" class="termref" href="#dt-is-types">in-scope schema types</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a> are initialized with a set of predefined schema types that is determined by the host language. This set may include some or all of the schema types in the namespace <code>http://www.w3.org/2001/XMLSchema</code>, represented in this document by the namespace prefix <code>xs</code>. The schema types in this namespace are defined in <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> and augmented by additional types defined in <a href="#xpath-datamodel-40">[XQuery and XPath Data Model (XDM) 4.0]</a>. An implementation that has based its type system on <a href="#XMLSchema10">[XML Schema 1.0]</a> is not required to support the <code>xs:dateTimeStamp</code> or <code>xs:error</code> types.</p><p>The schema types defined in <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#types-predefined">Section 2.8.3 Predefined Types</a><sup><small>DM</small></sup> are summarized below.</p><ol class="enumar"><li><p> [<a id="dt-untyped" title="xs:untyped">Definition</a>: <code>xs:untyped</code> is used as the <a title="type annotation" class="termref" href="#dt-type-annotation">type annotation</a> of an element node that has not been validated, or has been validated in <code>skip</code> mode.] No predefined schema types are derived from <code>xs:untyped</code>.</p></li><li><p> [<a id="dt-untypedAtomic" title="xs:untypedAtomic">Definition</a>: <code>xs:untypedAtomic</code> is an <a title="atomic type" class="termref" href="#dt-atomic-type">atomic type</a> that is used to denote untyped atomic data, such as text that has not been assigned a more specific type.] An attribute that has been validated in <code>skip</code> mode is represented in the <a title="data model" class="termref" href="#dt-datamodel">data model</a> by an attribute node with the <a title="type annotation" class="termref" href="#dt-type-annotation">type annotation</a><code>xs:untypedAtomic</code>. No predefined schema types are derived from <code>xs:untypedAtomic</code>.</p></li><li><p> [<a id="dt-dayTimeDuration" title="xs:dayTimeDuration">Definition</a>: <code>xs:dayTimeDuration</code> is derived by restriction from <code>xs:duration</code>. The lexical representation of <code>xs:dayTimeDuration</code> is restricted to contain only day, hour, minute, and second components.] </p></li><li><p> [<a id="dt-yearMonthDuration" title="xs:yearMonthDuration">Definition</a>: <code>xs:yearMonthDuration</code> is derived by restriction from <code>xs:duration</code>. The lexical representation of <code>xs:yearMonthDuration</code> is restricted to contain only year and month components.] </p></li><li><p> [<a id="dt-anyAtomicType" title="xs:anyAtomicType">Definition</a>: <code>xs:anyAtomicType</code> is an <a title="atomic type" class="termref" href="#dt-atomic-type">atomic type</a> that includes all atomic items (and no values that are not atomic). Its base type is <code>xs:anySimpleType</code> from which all simple types, including atomic, list, and union types, are derived. All primitive atomic types, such as <code>xs:decimal</code> and <code>xs:string</code>, have <code>xs:anyAtomicType</code> as their base type.] </p><div class="note"><p class="prefix"><b>Note:</b></p><p><code>xs:anyAtomicType</code> will not appear as the type of an actual value in an <a title="XDM instance" class="termref" href="#dt-data-model-instance">XDM instance</a>.</p></div></li><li><p> [<a id="dt-xs-error" title="xs:error">Definition</a>: <code>xs:error</code> is a simple type with no value space. It is defined in <a href="https://www.w3.org/TR/xmlschema11-1/#xsd-error">Section 3.16.7.3 xs:error </a><sup><small>XS11-1</small></sup> and can be used in the <a href="#id-sequencetype-syntax"><b>3.1 Sequence Types</b></a> to raise errors.] </p></li></ol><p>The relationships among the schema types in the <code>xs</code> namespace are illustrated in Figure 2. A more complete description of the XPath 4.0 type hierarchy can be found in <a href="https://qt4cg.org/specifications/xpath-functions-40/#datatypes">Section 1.8 Type System</a><sup><small>FO</small></sup>.</p><img src="types.jpg" alt="Type Hierarchy Diagram"><p>Figure 2: Hierarchy of Schema Types used in XPath 4.0.</p></div></div><div class="div1"><h2><a id="id-expressions"></a>4 Expressions</h2><p>This section discusses each of the basic kinds of expression. Each kind of expression has a name such as <code>PathExpr</code>, which is introduced on the left side of the grammar production that defines the expression. Since XPath 4.0 is a composable language, each kind of expression is defined in terms of other expressions whose operators have a higher precedence. In this way, the precedence of operators is represented explicitly in the grammar.</p><p>The order in which expressions are discussed in this document does not reflect the order of operator precedence. In general, this document introduces the simplest kinds of expressions first, followed by more complex expressions. For the complete grammar, see Appendix [<a href="#nt-bnf"><b>A XPath 4.0 Grammar</b></a>].</p><p><span class="xpath">The highest-level symbol in the XPath grammar is XPath.</span></p><a id="d3e13837"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-XPath"></a><code><a href="#prod-xpath40-XPath">XPath</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-Expr">Expr</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-Expr"></a><code><a href="#prod-xpath40-Expr">Expr</a></code></td><td>::=</td><td><code>(<a href="#doc-xpath40-ExprSingle">ExprSingle</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-ExprSingle"></a><code><a href="#prod-xpath40-ExprSingle">ExprSingle</a></code></td><td>::=</td><td><span style="display: none;" class="delete_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-OrExpr">OrExpr</a></code></span><span style="display: none;" class="add_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-PipelineExpr">PipelineExpr</a></code></span><span class="modify_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-OrExpr"><span class="deltaxml-old" style="background:#FF5555">OrExpr</span></a><a href="#doc-xpath40-PipelineExpr"><span class="deltaxml-new" style="background:#90EE90">PipelineExpr</span></a></code></span></td></tr></tbody></table><p>The XPath 4.0 operator that has lowest precedence is the <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a>, which is used to combine two operands to form a sequence. As shown in the grammar, a general expression (<a href="#doc-xpath40-Expr">Expr</a>) can consist of multiple <a href="#doc-xpath40-ExprSingle">ExprSingle</a> operands, separated by commas.</p><p>The name <a href="#doc-xpath40-ExprSingle">ExprSingle</a> denotes an expression that does not contain a top-level <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a> (despite its name, an <a href="#doc-xpath40-ExprSingle">ExprSingle</a> may evaluate to a sequence containing more than one item.)</p><p>The symbol <a href="#doc-xpath40-ExprSingle">ExprSingle</a> is used in various places in the grammar where an expression is not allowed to contain a top-level comma. For example, each of the arguments of a function call must be a <a href="#doc-xpath40-ExprSingle">ExprSingle</a>, because commas are used to separate the arguments of a function call.</p><p>After the comma, the expressions that have next lowest precedence are <span class="xpath"><a href="#doc-xpath40-ForExpr">ForExpr</a>, <a href="#doc-xpath40-LetExpr">LetExpr</a>, </span><a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a>, <a href="#doc-xpath40-IfExpr">IfExpr</a>, and <a href="#doc-xpath40-OrExpr">OrExpr</a>. Each of these expressions is described in a separate section of this document.</p><div class="div2"><h3><a id="comments"></a>4.1 Comments</h3><a id="d3e13934"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-Comment"></a><code><a href="#prod-xpath40-Comment">Comment</a></code></td><td>::=</td><td><code>"(:" (<a href="#doc-xpath40-CommentContents">CommentContents</a> | <a href="#doc-xpath40-Comment">Comment</a>)* ":)"</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-comments">gn: comments</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-CommentContents"></a><code><a href="#prod-xpath40-CommentContents">CommentContents</a></code></td><td>::=</td><td><code>(<a href="#prod-xpath40-Char">Char</a>+ - (Char* ('(:' | ':)') Char*))</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>Comments may be used to provide information relevant to programmers who read <span class="xpath">an expression</span>. Comments are lexical constructs only, and do not affect <span class="xpath">expression</span> processing.</p><p>Comments are strings, delimited by the symbols <code>(:</code> and <code>:)</code>. Comments may be nested.</p><p>A comment may be used anywhere <a title="ignorable whitespace" class="termref" href="#IgnorableWhitespace">ignorable whitespace</a> is allowed (see <a href="#DefaultWhitespaceHandling"><b>A.3.5.1 Default Whitespace Handling</b></a>).</p><p>The following is an example of a comment:</p><div class="exampleInner"><pre xml:space="preserve">(: Houston, we have a problem :)</pre></div></div><div class="div2"><h3><a id="id-primary-expressions"></a>4.2 Primary Expressions</h3><p> [<a id="dt-primary-expression" title="primary expression">Definition</a>: <b>Primary expressions</b> are the basic primitives of the language. They include literals, variable references, context value references, and function calls. A primary expression may also be created by enclosing any expression in parentheses, which is sometimes helpful in controlling the precedence of operators.] Map and Array Constructors are described in <a href="#id-maps"><b>4.13.1 Maps</b></a> and <a href="#id-arrays"><b>4.13.2 Arrays</b></a>. </p><a id="d3e14008"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-PrimaryExpr"></a><code><a href="#prod-xpath40-PrimaryExpr">PrimaryExpr</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-Literal">Literal</a><br>| <a href="#doc-xpath40-VarRef">VarRef</a><br>| <a href="#doc-xpath40-ParenthesizedExpr">ParenthesizedExpr</a><br>| <a href="#doc-xpath40-ContextValueRef">ContextValueRef</a><br>| <a href="#doc-xpath40-FunctionCall">FunctionCall</a><br>| <a href="#doc-xpath40-FunctionItemExpr">FunctionItemExpr</a><br>| <a href="#doc-xpath40-MapConstructor">MapConstructor</a><br>| <a href="#doc-xpath40-ArrayConstructor">ArrayConstructor</a><br>| <a href="#doc-xpath40-StringTemplate">StringTemplate</a><br>| <a href="#doc-xpath40-UnaryLookup">UnaryLookup</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-FunctionItemExpr"></a><code><a href="#prod-xpath40-FunctionItemExpr">FunctionItemExpr</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-NamedFunctionRef">NamedFunctionRef</a> | <a href="#doc-xpath40-InlineFunctionExpr">InlineFunctionExpr</a></code></td></tr></tbody></table><div class="div3"><h4><a id="id-literals"></a>4.2.1 Literals</h4><a id="d3e14079"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-Literal"></a><code><a href="#prod-xpath40-Literal">Literal</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-NumericLiteral">NumericLiteral</a> | <a href="#doc-xpath40-StringLiteral">StringLiteral</a></code></td></tr></tbody></table><p> [<a id="dt-literal" title="literal">Definition</a>: A <b>literal</b> is a direct syntactic representation of an atomic item.] XPath 4.0 supports two kinds of literals: numeric literals and string literals.</p><div class="div4"><h5><a id="id-numeric-literals"></a>4.2.1.1 Numeric Literals</h5><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-filter-expression">⬇</a>&nbsp;<a href="#id-function-coercion">⬆</a></p><ol><li><p> Numeric literals can now be written in hexadecimal or binary notation; and underscores can be included for readability. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/429">429</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/433">433</a>&nbsp;25 April 2023]</i></p></li></ol></div><a id="d3e14105"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-NumericLiteral"></a><code><a href="#prod-xpath40-NumericLiteral">NumericLiteral</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-IntegerLiteral">IntegerLiteral</a> | <a href="#doc-xpath40-HexIntegerLiteral">HexIntegerLiteral</a> | <a href="#doc-xpath40-BinaryIntegerLiteral">BinaryIntegerLiteral</a> | <a href="#doc-xpath40-DecimalLiteral">DecimalLiteral</a> | <a href="#doc-xpath40-DoubleLiteral">DoubleLiteral</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-IntegerLiteral"></a><code><a href="#prod-xpath40-IntegerLiteral">IntegerLiteral</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-Digits">Digits</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-HexIntegerLiteral"></a><code><a href="#prod-xpath40-HexIntegerLiteral">HexIntegerLiteral</a></code></td><td>::=</td><td><code>"0x" <a href="#doc-xpath40-HexDigits">HexDigits</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-BinaryIntegerLiteral"></a><code><a href="#prod-xpath40-BinaryIntegerLiteral">BinaryIntegerLiteral</a></code></td><td>::=</td><td><code>"0b" <a href="#doc-xpath40-BinaryDigits">BinaryDigits</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-DecimalLiteral"></a><code><a href="#prod-xpath40-DecimalLiteral">DecimalLiteral</a></code></td><td>::=</td><td><code>("." <a href="#doc-xpath40-Digits">Digits</a>) | (<a href="#doc-xpath40-Digits">Digits</a> "." <a href="#doc-xpath40-Digits">Digits</a>?)</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-DoubleLiteral"></a><code><a href="#prod-xpath40-DoubleLiteral">DoubleLiteral</a></code></td><td>::=</td><td><code>(("." <a href="#doc-xpath40-Digits">Digits</a>) | (<a href="#doc-xpath40-Digits">Digits</a> ("." <a href="#doc-xpath40-Digits">Digits</a>?)?)) [eE] [+-]? <a href="#doc-xpath40-Digits">Digits</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-Digits"></a><code><a href="#prod-xpath40-Digits">Digits</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-DecDigit">DecDigit</a> ((<a href="#doc-xpath40-DecDigit">DecDigit</a> | "_")* <a href="#doc-xpath40-DecDigit">DecDigit</a>)?</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-DecDigit"></a><code><a href="#prod-xpath40-DecDigit">DecDigit</a></code></td><td>::=</td><td><code>[0-9]</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-HexDigits"></a><code><a href="#prod-xpath40-HexDigits">HexDigits</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-HexDigit">HexDigit</a> ((<a href="#doc-xpath40-HexDigit">HexDigit</a> | "_")* <a href="#doc-xpath40-HexDigit">HexDigit</a>)?</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-HexDigit"></a><code><a href="#prod-xpath40-HexDigit">HexDigit</a></code></td><td>::=</td><td><code>[0-9a-fA-F]</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-BinaryDigits"></a><code><a href="#prod-xpath40-BinaryDigits">BinaryDigits</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-BinaryDigit">BinaryDigit</a> ((<a href="#doc-xpath40-BinaryDigit">BinaryDigit</a> | "_")* <a href="#doc-xpath40-BinaryDigit">BinaryDigit</a>)?</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-BinaryDigit"></a><code><a href="#prod-xpath40-BinaryDigit">BinaryDigit</a></code></td><td>::=</td><td><code>[01]</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>The value of a numeric literal is determined as follows (taking the rules in order):</p><ol class="enumar"><li><p>Underscore characters are stripped out. Underscores may be included in a numeric literal to aid readability, but have no effect on the value. For example, <code>1_000_000</code> is equivalent to <code>1000000</code>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Underscores must not appear at the beginning or end of a sequence of digits, only in intermediate positions. Multiple adjacent underscores are allowed.</p></div></li><li><p>A <code>HexIntegerLiteral</code> represents a non-negative integer expressed in hexadecimal: for example <code>0xffff</code> represents the integer 65535, and <code>0xFFFF_FFFF</code> represents the integer 4294967295.</p></li><li><p>A <code>BinaryIntegerLiteral</code> represents a non-negative integer expressed in binary: for example <code>0b101</code> represents the integer 5, and <code>0b1111_1111</code> represents the integer 255.</p></li><li><p>The value of a <b>numeric literal</b> containing no <code>.</code> and no <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:integer</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:integer</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li><li><p>The value of a numeric literal containing <code>.</code> but no <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:decimal</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:decimal</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li><li><p>The value of a numeric literal containing an <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:double</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:double</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li></ol><div class="note"><p class="prefix"><b>Note:</b></p><p>The value of a numeric literal is always non-negative. An expression may appear to include a negative number such as <code>-1</code>, but this is technically an arithmetic expression comprising a unary minus operator followed by a numeric literal.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The effect of the above rules is that in the case of an integer or decimal literal, a dynamic error [<a href="https://qt4cg.org/specifications/xpath-functions-40/#ERRFOAR0002" title="err:FOAR0002">err:FOAR0002</a>]<sup><small>FO40</small></sup> will generally be raised if the literal is outside the range of values supported by the implementation (other options are available: see <a href="https://qt4cg.org/specifications/xpath-functions-40/#op.numeric">Section 4.2 Arithmetic operators on numeric values</a><sup><small>FO</small></sup> for details.)</p><p class="xpath">The XML Schema specification allows implementations to impose a limit (which must not be less than 18 digits) on the size of integer and decimal values. The full range of values of built-in subtypes of <code>xs:integer</code>, such as <code>xs:long</code> and <code>xs:unsignedLong</code>, can be supported only if the limit is 20 digits or higher. Negative numbers such as the minimum value of <code>xs:long</code> (<code>-9223372036854775808</code>) are technically unary expressions rather than literals, but implementations may prefer to ensure that they are expressible.</p></div><p>Here are some examples of numeric literals:</p><ul><li><p><code>12</code> denotes the <code>xs:integer</code> value twelve.</p></li><li><p><code>1_000_000</code> denotes the <code>xs:integer</code> value one million.</p></li><li><p><code>12.5</code> denotes the <code>xs:decimal</code> value twelve and one half.</p></li><li><p><code>3.14159_26535_89793e0</code> is an <code>xs:double</code> value representing the mathematical constant <var>π</var> to 15 decimal places. </p></li><li><p><code>125E2</code> denotes the <code>xs:double</code> value twelve thousand, five hundred.</p></li><li><p><code>0xffff</code> denotes the <code>xs:integer</code> value 65535.</p></li><li><p><code>0b1000_0001</code> denotes the <code>xs:integer</code> value 129.</p></li></ul></div><div class="div4"><h5><a id="id-string-literal"></a>4.2.1.2 String Literals</h5><a id="d3e14489"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-StringLiteral"></a><code><a href="#prod-xpath40-StringLiteral">StringLiteral</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-AposStringLiteral">AposStringLiteral</a> | <a href="#doc-xpath40-QuotStringLiteral">QuotStringLiteral</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-AposStringLiteral"></a><code><a href="#prod-xpath40-AposStringLiteral">AposStringLiteral</a></code></td><td>::=</td><td><code>"'" (<a href="#doc-xpath40-EscapeApos">EscapeApos</a> | [^'])* "'"</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-QuotStringLiteral"></a><code><a href="#prod-xpath40-QuotStringLiteral">QuotStringLiteral</a></code></td><td>::=</td><td><code>'"' (<a href="#doc-xpath40-EscapeQuot">EscapeQuot</a> | [^"])* '"'</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-EscapeQuot"></a><code><a href="#prod-xpath40-EscapeQuot">EscapeQuot</a></code></td><td>::=</td><td><code>'""'</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-EscapeApos"></a><code><a href="#prod-xpath40-EscapeApos">EscapeApos</a></code></td><td>::=</td><td><code>"''"</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>The value of a <b>string literal</b> is an atomic item whose type is <code>xs:string</code> and whose value is the string denoted by the characters between the delimiting apostrophes or quotation marks. If the literal is delimited by apostrophes, two adjacent apostrophes within the literal are interpreted as a single apostrophe. Similarly, if the literal is delimited by quotation marks, two adjacent quotation marks within the literal are interpreted as one quotation mark.</p><p>Here are some examples of string literals:</p><ul><li><p><code>"He said, ""I don't like it."""</code> denotes a string containing two quotation marks and one apostrophe.</p></li><li><p>In XQuery, the string literal <code>"&amp;lt;"</code> denotes a string of length 1 containing the single character <code>"&lt;"</code>. In XPath, the string literal <code>"&amp;lt;"</code> denotes a string of length 4 containing the four characters <code>"&amp;"</code>, <code>"l"</code>, <code>"t"</code>, <code>";"</code>. (However, when the XPath expression is embedded in an XML document, the sequence <code>"&amp;lt;"</code> will typically have already been converted to <code>"&lt;"</code> by the XML parser.)</p></li></ul><div class="note"><p class="prefix"><b>Note:</b></p><p>When XPath or XQuery expressions are embedded in contexts where quotation marks have special significance, such as inside XML attributes, or in string literals in a host language such as Java or C#, then additional escaping may be needed.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>Fixed string values can also be written as string templates: see <a href="#id-string-templates"><b>4.9.2 String Templates</b></a>. A string template with no enclosed expressions, such as <code>`Jamaica`</code> evaluates to the same value as the string literals <code>"Jamaica"</code> or <code>'Jamaica'</code>. A string template can contain both single and double quotation marks: <code>`He said: "I don't like it"`</code>. However, there there are some subtle differences:</p><ul><li><p>In string literals, the treatment of character and entity references such as <code>&amp;amp;</code> varies between XQuery and XPath; in string templates, such references are not expanded in either language.</p></li><li><p>String templates can only be used where an expression is expected. String literals are also used in some non-expression contexts, for example in defining an enumeration type: see <a href="#id-enumeration-types"><b>3.2.6 Enumeration Types</b></a>.</p></li><li><p>Curly brackets (<span class="unicode-codepoint">U+007B</span> (<span class="unicode-name">LEFT CURLY BRACKET</span>, <code>{</code>) and <span class="unicode-codepoint">U+007D</span> (<span class="unicode-name">RIGHT CURLY BRACKET</span>, <code>}</code>) ) and backticks (<span class="unicode-codepoint">U+0060</span> (<span class="unicode-name">GRAVE ACCENT, BACKTICK</span>, <code>`</code>) ) have a reserved meaning in string templates.</p></li></ul></div></div><div class="div4"><h5><a id="id-constants-other-types"></a>4.2.1.3 Constants of Other Types</h5><p> The <code>xs:boolean</code> values <code>true</code> and <code>false</code> can be constructed by calls to the <a title="system function" class="termref" href="#dt-system-function">system functions</a><code>fn:true()</code> and <code>fn:false()</code>, respectively. </p><p>Values of other simple types can be constructed by calling the <a title="constructor function" class="termref" href="#dt-constructor-function">constructor function</a> for the given type. The constructor functions for XML Schema built-in types are defined in <a href="https://qt4cg.org/specifications/xpath-functions-40/#constructor-functions-for-xsd-types">Section 20.1 Constructor functions for XML Schema built-in atomic types</a><sup><small>FO</small></sup>. In general, the name of a constructor function for a given type is the same as the name of the type (including its namespace). For example:</p><ul><li><p><code>xs:integer("12")</code> returns the integer value twelve.</p></li><li><p><code>xs:date("2001-08-25")</code> returns an item whose type is <code>xs:date</code> and whose value represents the date 25th August 2001.</p></li><li><p><code>xs:dayTimeDuration("PT5H")</code> returns an item whose type is <code>xs:dayTimeDuration</code> and whose value represents a duration of five hours.</p></li></ul><p>Constructor functions can also be used to create special values that have no literal representation, as in the following examples: </p><ul><li><p><code>xs:float("NaN")</code> returns the special floating-point value, "Not a Number."</p></li><li><p><code>xs:double("INF")</code> returns the special double-precision value, "positive infinity."</p></li></ul><p>Constructor functions are available for all simple types, including union types. For example, if <code>my:dt</code> is a user-defined union type whose member types are <code>xs:date</code>, <code>xs:time</code>, and <code>xs:dateTime</code>, then the expression <code>my:dt("2011-01-10")</code> creates an atomic item of type <code>xs:date</code>. The rules follow XML Schema validation rules for union types: the effect is to choose the first member type that accepts the given string in its lexical space.</p><p>It is also possible to construct values of various types by using a <code>cast</code> expression. For example:</p><ul><li><p><code>9 cast as hatsize</code> returns the atomic item <code>9</code> whose type is <code>hatsize</code>.</p></li></ul></div></div><div class="div3"><h4><a id="id-variables"></a>4.2.2 Variable References</h4><a id="d3e14744"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-VarRef"></a><code><a href="#prod-xpath40-VarRef">VarRef</a></code></td><td>::=</td><td><code>"$" <a href="#doc-xpath40-EQName">EQName</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e13737.doc-xpath40-EQName"></a><code>EQName</code></td><td>::=</td><td><code><a href="#doc-xpath40-QName">QName</a> | <a href="#doc-xpath40-URIQualifiedName">URIQualifiedName</a></code></td></tr></tbody></table><p> [<a id="dt-variable-reference" title="variable reference">Definition</a>: A <b>variable reference</b> is an EQName preceded by a $-sign.] An unprefixed variable reference is in no namespace. Two variable references are equivalent if their <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QNames</a> are equal (as defined by the <code>eq</code> operator). The scope of a variable binding is defined separately for each kind of expression that can bind variables.</p><p>Every variable reference must match a name in the <a title="in-scope variables" class="termref" href="#dt-in-scope-variables">in-scope variables</a>. </p><p>Every variable binding has a static scope. The scope defines where references to the variable can validly occur. It is a <a title="static error" class="termref" href="#dt-static-error">static error</a> [<a href="#ERRXPST0008" title="err:XPST0008">err:XPST0008</a>] to reference a variable that is not in scope. If a variable is bound in the <a title="static context" class="termref" href="#dt-static-context">static context</a> for an expression, that variable is in scope for the entire expression except where it is occluded by another binding that uses the same name within that scope.</p><p> At evaluation time, the value of a variable reference is the value to which the relevant variable is bound.</p></div><div class="div3"><h4><a id="id-context-value-references"></a>4.2.3 Context Value References</h4><a id="d3e14795"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-ContextValueRef"></a><code><a href="#prod-xpath40-ContextValueRef">ContextValueRef</a></code></td><td>::=</td><td><code>"."</code></td></tr></tbody></table><p>A <b>context value reference</b> evaluates to the <a title="context value" class="termref" href="#dt-context-value">context value</a>.</p><p>In many syntactic contexts, the context value will be a single item. For example this applies on the right-hand side of the <code>/</code> or <code>!</code> operators, or within a <a href="#doc-xpath40-Predicate">Predicate</a>.</p><p>If the <a title="context value" class="termref" href="#dt-context-value">context value</a> is <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#dt-absent">absent</a><sup><small>DM</small></sup>, a context value reference raises a <a title="type error" class="termref" href="#dt-type-error">type error</a> [<a href="#ERRXPDY0002" title="err:XPDY0002">err:XPDY0002</a>].</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Being absent is not the same thing as being empty.</p></div></div><div class="div3"><h4><a id="id-paren-expressions"></a>4.2.4 Parenthesized Expressions</h4><a id="d3e14831"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-ParenthesizedExpr"></a><code><a href="#prod-xpath40-ParenthesizedExpr">ParenthesizedExpr</a></code></td><td>::=</td><td><code>"(" <a href="#doc-xpath40-Expr">Expr</a>? ")"</code></td></tr></tbody></table><p>Parentheses may be used to override the precedence rules. For example, the expression <code>(2 + 4) * 5</code> evaluates to thirty, since the parenthesized expression <code>(2 + 4)</code> is evaluated first and its result is multiplied by five. Without parentheses, the expression <code>2 + 4 * 5</code> evaluates to twenty-two, because the multiplication operator has higher precedence than the addition operator.</p><p>Empty parentheses are used to denote an empty sequence, as described in <a href="#construct_seq"><b>4.7.1 Sequence Concatenation</b></a>.</p></div><div class="div3"><h4><a id="id-enclosed-expr"></a>4.2.5 Enclosed Expressions</h4><p><a id="d3e14859"></a></p><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-EnclosedExpr"></a><code><a href="#prod-xpath40-EnclosedExpr">EnclosedExpr</a></code></td><td>::=</td><td><code>"{" <a href="#doc-xpath40-Expr">Expr</a>? "}"</code></td></tr></tbody></table><p> [<a id="dt-enclosed-expression" title="enclosed expression">Definition</a>: An <b>enclosed expression</b> is an instance of the <a href="#doc-xpath40-EnclosedExpr">EnclosedExpr</a> production, which allows an optional expression within curly brackets.] [<a id="dt-content-expression" title="content expression">Definition</a>: In an <a title="enclosed expression" class="termref" href="#dt-enclosed-expression">enclosed expression</a>, the optional expression enclosed in curly brackets is called the <b>content expression</b>.] If the <a title="content expression" class="termref" href="#dt-content-expression">content expression</a> is not provided explicitly, the content expression is <code>()</code>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Despite the name, an enclosed expression is not actually an expression in its own right; rather it is a construct that is used in the grammar of many other expressions.</p></div></div></div><div class="div2"><h3><a id="id-postfix-expression"></a>4.3 Postfix Expressions</h3><a id="d3e14895"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-PostfixExpr"></a><code><a href="#prod-xpath40-PostfixExpr">PostfixExpr</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-PrimaryExpr">PrimaryExpr</a> | <a href="#doc-xpath40-FilterExpr">FilterExpr</a> | <a href="#doc-xpath40-DynamicFunctionCall">DynamicFunctionCall</a> | <a href="#doc-xpath40-LookupExpr">LookupExpr</a> | <a href="#doc-xpath40-FilterExprAM">FilterExprAM</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e13859.doc-xpath40-FilterExpr"></a><code>FilterExpr</code></td><td>::=</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Predicate">Predicate</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e13860.doc-xpath40-DynamicFunctionCall"></a><code>DynamicFunctionCall</code></td><td>::=</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-PositionalArgumentList">PositionalArgumentList</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e13861.doc-xpath40-LookupExpr"></a><code>LookupExpr</code></td><td>::=</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Lookup">Lookup</a></code></td></tr></tbody></table><p>A postfix expression takes one of the following forms:</p><ul><li><p> [<a id="dt-filter-expression" title="filter expression">Definition</a>: A <b>filter expression</b> is an expression in the form <code>E1[E2]</code>: its effect is to return those items from the value of <code>E1</code> that satisfy the predicate in E2.] </p><p>Filter expressions are described in <a href="#id-filter-expression"><b>4.4 Filter Expressions</b></a>.</p><p>An example of a filter expression is <code>(1 to 100)[. mod 2 = 0]</code> which returns all even numbers in the range 1 to 100.</p><p>The base expression <code>E1</code> can itself be a postfix expression, so multiple predicates are allowed, in the form <code>E1[E2][E3][E4]</code>.</p></li><li><p>An expression (other than a raw EQName) followed by an argument list in parentheses (that is, <code>E1(E2, E3, ...)</code>) is referred to as a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-invocation">dynamic function call</a>. Its effect is to evaluate <code>E1</code> to obtain a function, and then call that function, with <code>E2</code>, <code>E3</code>, <code>...</code> as arguments. Dynamic function calls are described in <a href="#id-dynamic-function-invocation"><b>4.5.2.1 Dynamic Function Calls</b></a>.</p><p>An example of a dynamic function call is <code>$f("a", 2)</code> where the value of variable <code>$f</code> must be a function item.</p></li><li><p>A <code>lookup-expression</code> takes the form <code>E1?K</code>, where <code>E1</code> is an expression returning a sequence of maps or arrays, and <code>K</code> is a key specifier, which indicates which entries in a map, or members in an array, should be selected.</p><p>Lookup expressions are described in <a href="#id-postfix-lookup"><b>4.13.3.1 Postfix Lookup Expressions</b></a>.</p><p>An example of a lookup expression is <code>$emp?name</code>, where the value of variable <code>$emp</code> is a map, and the string <code>"name"</code> is the key of one of the entries in the map.</p></li></ul><p>Postfix expressions are evaluated from left-to-right. For example, the expression <code>$E1[E2]?(E3)(E4)</code> is evaluated by first evaluating the filter expression <code>$E1[E2]</code> to produce a sequence of maps and arrays (say <code>$S</code>), then evaluating the lookup expression <code>$S?(E3)</code> to produce a function item (say <code>$F</code>), then evaluating the dynamic function call <code>$F(E4)</code> to produce the final result.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>The grammar for postfix expressions is defined here in a way designed to link clearly to the semantics of the different kinds of expression. For parsing purposes, the equivalent production rule:</p><div class="exampleInner"><pre xml:space="preserve">PostfixExpr := PrimaryExpr (Predicate | PositionalArgumentList | Lookup)*</pre></div><p>(as used in XPath 3.1) is probably more convenient.</p></div></div><div class="div2"><h3><a id="id-filter-expression"></a>4.4 Filter Expressions</h3><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-function-calls">⬇</a>&nbsp;<a href="#id-numeric-literals">⬆</a></p><ol><li><p> The value of a predicate in a filter expression can now be a sequence of integers. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/816">816</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/996">996</a>&nbsp;6 February 2024]</i></p></li></ol></div><a id="d3e15074"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-FilterExpr"></a><code><a href="#prod-xpath40-FilterExpr">FilterExpr</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Predicate">Predicate</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-Predicate"></a><code><a href="#prod-xpath40-Predicate">Predicate</a></code></td><td>::=</td><td><code>"[" <a href="#doc-xpath40-Expr">Expr</a> "]"</code></td></tr></tbody></table><p>A filter expression consists of a base expression followed by a predicate, which is an expression written in square brackets. The result of the filter expression consists of the items returned by the base expression, filtered by applying the predicate to each item in turn. The ordering of the items returned by a filter expression is the same as their order in the result of the primary expression.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Where the expression before the square brackets is a <a href="#doc-xpath40-ReverseStep">ReverseStep</a> or <a href="#doc-xpath40-ForwardStep">ForwardStep</a>, the expression is technically not a filter expression but an <a href="#doc-xpath40-AxisStep">AxisStep</a>. There are minor differences in the semantics: see <a href="#id-predicate"><b>4.6.5 Predicates within Steps</b></a></p></div><p>Here are some examples of filter expressions:</p><ul><li><p>Given a sequence of products in a variable, return only those products whose price is greater than 100.</p><div class="exampleInner"><pre xml:space="preserve">$products[price gt 100]</pre></div></li><li><p>List all the integers from 1 to 100 that are divisible by 5. (See <a href="#construct_seq"><b>4.7.1 Sequence Concatenation</b></a> for an explanation of the <code>to</code> operator.)</p><div class="exampleInner"><pre xml:space="preserve">(1 to 100)[. mod 5 eq 0]</pre></div></li><li><p>The result of the following expression is the integer 25:</p><div class="exampleInner"><pre xml:space="preserve">(21 to 29)[5]</pre></div></li><li><p>The following example returns the fifth through ninth items in the sequence bound to variable <code>$orders</code>.</p><div class="exampleInner"><pre xml:space="preserve">$orders[5 to 9]</pre></div></li><li><p>The following example illustrates the use of a filter expression as a <a title="step" class="termref" href="#dt-step">step</a> in a <a title="path expression" class="termref" href="#dt-path-expression">path expression</a>. It returns the last chapter or appendix within the book bound to variable <code>$book</code>:</p><div class="exampleInner"><pre xml:space="preserve">$book/(chapter | appendix)[last()]</pre></div></li></ul><p>For each item in the input sequence, the predicate expression is evaluated using an <b>inner focus</b>, defined as follows: The context value is the item currently being tested against the predicate. The context size is the number of items in the input sequence. The context position is the position of the context value within the input sequence. </p><p>For each item in the input sequence, the result of the predicate expression is coerced to an <code>xs:boolean</code> value, called the <a title="predicate truth value" class="termref" href="#dt-predicate-truth-value">predicate truth value</a>, as described below. Those items for which the predicate truth value is <code>true</code> are retained, and those for which the predicate truth value is <code>false</code> are discarded.</p><p> [<a id="dt-predicate-truth-value" title="predicate truth value">Definition</a>: The <b>predicate truth value</b> of a value <code>$V</code> is the result of the expression <code>if ($V instance of xs:numeric+) then ($V = position()) else fn:boolean($V)</code>.] </p><p>Expanding this definition, the predicate truth value can be obtained by applying the following rules, in order:</p><ol class="enumar"><li><p>If the value <var>V</var> of the predicate expression is a sequence whose first item is an instance of the type <code>xs:numeric</code>, then:</p><ol class="enumla"><li><p><var>V</var> must be an instance of the type <code>xs:numeric+</code> (that is, every item in <var>V</var> must be numeric). A type error [<a href="https://qt4cg.org/specifications/xpath-functions-40/#ERRFORG0006" title="err:FORG0006">err:FORG0006</a>]<sup><small>FO40</small></sup> is raised if this is not the case.</p></li><li><p>The predicate truth value is <code>true</code> if <var>V</var> is equal (by the <code>=</code> operator) to the <b>context position</b>, and is <code>false</code> otherwise.</p></li></ol><p>In effect this means that an item in the input sequence is selected if its position in the sequence is equal to one or more of the numeric values in the predicate. For example, the predicate <code>[3 to 5]</code> is true for the third, fourth, and fifth items in the input sequence.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>It is possible, though not generally useful, for the value of a numeric predicate to depend on the focus, and thus to differ for different items in the input sequence. For example, the predicate <code>[xs:integer(@seq)]</code> selects those items in the input sequence whose <code>@seq</code> attribute is numerically equal to their position in the input sequence.</p><p>It is also possible, and again not generally useful, for the value of the predicate to be numeric for some items in the input sequence, and boolean for others. For example, the predicate <code>[@special otherwise last()]</code> is true for an item that either has an <code>@special</code> attribute, or is the last item in the input sequence.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The truth value of a numeric predicate does not depend on the order of the numbers in <var>V</var>. The predicates <code>[ 1, 2, 3 ]</code> and <code>[ 3, 2, 1 ]</code> have exactly the same effect. The items in the result of a filter expression always retain the ordering of the input sequence.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The truth value of a numeric predicate whose value is non-integral or non-positive is always false.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>Beware that using boolean operators (<code>and</code>, <code>or</code>, <code>not()</code>) with numeric values may not have the intended effect. For example the predicate <code>[1 or last()]</code> selects every item in the sequence, because <code>or</code> operates on the <a title="effective boolean value" class="termref" href="#dt-ebv">effective boolean value</a> of its operands. The required effect can be achieved with the predicate <code>[1, last()]</code>.</p></div></li><li><p>Otherwise, the predicate truth value is the <a title="effective boolean value" class="termref" href="#dt-ebv">effective boolean value</a> of the predicate expression.</p></li></ol></div><div class="div2"><h3><a id="id-functions"></a>4.5 Functions</h3><p>Functions in XPath 4.0 arise in two ways:</p><ul><li><p>A <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> contains information about a family of functions with the same name and a defined arity range. These functions are in most cases known statically (they appear in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a>), but there may be further function definitions that are known only dynamically (appearing in the <a title="dynamically known function definitions" class="termref" href="#dt-dynamically-known-function-definitions">dynamically known function definitions</a>).</p></li><li><p><a title="function item" class="termref" href="#dt-function-item">Function items</a> are XDM items that can be called using a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-call">dynamic function call</a>. They are values that can be bound to variables, passed as arguments, returned as function results, and generally manipulated in the same way as other XDM values.</p></li></ul><p>The functions defined by a statically known <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> can be invoked using a <a title="static function call" class="termref" href="#dt-static-function-call">static function call</a>. <a title="function item" class="termref" href="#dt-function-item">Function items</a> corresponding to these definitions can also be obtained, as dynamic values, by evaluating a <a title="named function reference" class="termref" href="#dt-named-function-ref">named function reference</a>. <a title="function item" class="termref" href="#dt-function-item">Function items</a> can also be obtained using the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-function-lookup"><code>fn:function-lookup</code></a> function: in this case the function name and arity do not need to be known statically, and the function definition need not be present in the <a title="static context" class="termref" href="#dt-static-context">static context</a>, so long as it is in the <a title="dynamic context" class="termref" href="#dt-dynamic-context">dynamic context</a>.</p><p>Static and dynamic function calls are described in the following sections.</p><div class="div3"><h4><a id="id-static-functions"></a>4.5.1 Static Function Calls</h4><p>The <a title="static context" class="termref" href="#dt-static-context">static context</a> for an expression includes a set of <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a>. Every <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context has a name (which is an <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a>) and an <a title="arity range" class="termref" href="#dt-arity-range">arity range</a>, which is a range of permitted arities for calls on that function. Two <a title="function definition" class="termref" href="#dt-function-definition">function definitions</a> having the same name must not have overlapping arity ranges. This means that for a given static function call, it is possible to identify the target function definition in the static context unambiguously from knowledge of the function name and the number of supplied arguments.</p><p>A <a title="static function call" class="termref" href="#dt-static-function-call">static function call</a> is bound to a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context by matching the name and arity. If the function call has <var>P</var> positional arguments followed by <var>K</var> keyword arguments, then the required arity is <var>P+K</var>, and the static context must include a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> whose name matches the <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a> in the function call, and whose <a title="arity range" class="termref" href="#dt-arity-range">arity range</a> includes this required arity. This is the function chosen to be called. The result of the function is obtained by evaluating the expression that forms its implementation, with a dynamic context that provides values for all the declared parameters, initialized as described in <a href="#id-eval-static-function-call"><b>4.5.1.2 Evaluating Static Function Calls</b></a> below.</p><p>Similarly, a function reference of the form <code>f#N</code> binds to a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context whose name matches <var>f</var> where <code>MinP ≤ N and MaxP ≥ N</code>. The result of evaluating a function reference is a <a title="function item" class="termref" href="#dt-function-item">function item</a> which can be called using a dynamic function call. Function items are never variadic and their arguments are always supplied positionally. For example, the function reference <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-concat"><code>fn:concat#3</code></a> returns a function item with arity 3, which is always called by supplying three positional arguments, and whose effect is the same as a static call on <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-concat"><code>fn:concat</code></a> with three positional arguments. </p><p>The detailed rules for evaluating static function calls and function references are defined in subsequent sections.</p><div class="div4"><h5><a id="id-function-calls"></a>4.5.1.1 Static Function Call Syntax</h5><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-inline-func">⬇</a>&nbsp;<a href="#id-filter-expression">⬆</a></p><ol><li><p> Keyword arguments are allowed on static function calls, as well as positional arguments. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/155">155</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/159">159</a>&nbsp;30 September 2020]</i></p></li></ol></div><a id="d3e15398"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-FunctionCall"></a><code><a href="#prod-xpath40-FunctionCall">FunctionCall</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-EQName">EQName</a><a href="#doc-xpath40-ArgumentList">ArgumentList</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-reserved-function-names">xgc: reserved-function-names</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-parens">gn: parens</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-ArgumentList"></a><code><a href="#prod-xpath40-ArgumentList">ArgumentList</a></code></td><td>::=</td><td><code>"(" ((<a href="#doc-xpath40-PositionalArguments">PositionalArguments</a> ("," <a href="#prod-xpath40-KeywordArguments">KeywordArguments</a>)?) | <a href="#prod-xpath40-KeywordArguments">KeywordArguments</a>)? ")"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e14299.doc-xpath40-PositionalArguments"></a><code>PositionalArguments</code></td><td>::=</td><td><code>(<a href="#doc-xpath40-Argument">Argument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-Argument"></a><code><a href="#prod-xpath40-Argument">Argument</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-ExprSingle">ExprSingle</a> | <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-ArgumentPlaceholder"></a><code><a href="#prod-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td><td>::=</td><td><code>"?"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e14302.doc-xpath40-KeywordArguments"></a><code>KeywordArguments</code></td><td>::=</td><td><code>(<a href="#doc-xpath40-KeywordArgument">KeywordArgument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-KeywordArgument"></a><code><a href="#prod-xpath40-KeywordArgument">KeywordArgument</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-EQName">EQName</a> ":=" <a href="#doc-xpath40-Argument">Argument</a></code></td></tr></tbody></table><p> [<a id="dt-static-function-call" title="static function call">Definition</a>: A <b>static function call</b> consists of an EQName followed by a parenthesized list of zero or more arguments.] </p><p>The argument list consists of zero or more positional arguments, followed by zero or more keyword arguments.</p><p> [<a id="dt-arg-expr" title="argument expression">Definition</a>: An argument to a function call is either an <b>argument expression</b> or an <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a> (<code>?</code>); in both cases it may either be supplied positionally, or identified by a name (called a keyword).] </p><p>This section is concerned with static function calls in which none of the arguments are <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholders</a>. Calls using one or more <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholders</a> are covered in the section <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p>If the function name supplied in a static function call is an unprefixed <a title="lexical QName" class="termref" href="#dt-qname">lexical QName</a>, it is expanded using the <a title="default function namespace" class="termref" href="#dt-default-function-namespace">default function namespace</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a>. </p><p> The <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a> used as the function name and the number of arguments used in the static function call (the required arity) must match the name and arity range of a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a><span> using the rules defined in the previous section</span>; if there is no match, a <a title="static error" class="termref" href="#dt-static-error">static error</a> is raised [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>]. </p><p>Evaluation of static function calls is described in <a href="#id-eval-static-function-call"><b>4.5.1.2 Evaluating Static Function Calls</b></a> .</p><p>Since the arguments of a function call are separated by commas, any <a title="argument expression" class="termref" href="#dt-arg-expr">argument expression</a> that contains a top-level <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a> must be enclosed in parentheses. Here are some illustrative examples of static function calls:</p><ul><li><p><code>my:three-argument-function(1, 2, 3)</code> denotes a static function call with three <span>positional</span> arguments. <span>The corresponding function declaration must define at least three parameters, and may define more, provided they are optional.</span></p></li><li><p><code>my:two-argument-function((1, 2), 3)</code> denotes a static function call with two arguments, the first of which is a sequence of two values. <span>The corresponding function declaration must define at least two parameters, and may define more, provided they are optional.</span></p></li><li><p><code>my:two-argument-function(1, ())</code> denotes a static function call with two arguments, the second of which is an empty sequence.</p></li><li><p><code>my:one-argument-function((1, 2, 3))</code> denotes a static function call with one argument that is a sequence of three values. </p></li><li><p><code>my:one-argument-function(( ))</code> denotes a static function call with one argument that is an empty sequence.</p></li><li><p><code>my:zero-argument-function( )</code> denotes a static function call with zero arguments.</p></li><li><p><code>lang(node := $n, language := 'de')</code> is a static function call with two keyword arguments. The corresponding function declaration defines two parameters, a required parameter <code>language</code> and an optional parameter <code>node</code>. This call supplies values for both parameters. It is equivalent to the call <code>fn:lang('de', $n)</code>. Note that the keyword arguments are in a different order from the parameter declarations. </p></li><li><p><code>sort(//employee, key := fn($e) { xs:decimal($e/salary) })</code> is a static function call with one positional argument and one keyword argument. The corresponding function declaration defines three parameters, a required parameter <code>$input</code>, an optional parameter <code>$collation</code>, and an optional parameter <code>$key</code> This call supplies values for the first and third parameters, leaving the second parameter (<code>$collation</code>) to take its default value. The default value of the <code>$collation</code> parameter is given as <code>fn:default-collation()</code>, so the value supplied to the function is the default collation from the dynamic context of the caller. It is equivalent to the call <code>fn:sort(//employee, fn:default-collation(), fn($e) { xs:decimal($e/salary) })</code>. </p></li></ul><p>An <code>EQName</code> in a <code>KeywordArgument</code> is expanded to a QName value; if there is no prefix, then the name is in no namespace (otherwise the prefix is resolved in the usual way). The keywords used in a function call (after expansion to QNames) must be distinct [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>]; [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>].</p></div><div class="div4"><h5><a id="id-eval-static-function-call"></a>4.5.1.2 Evaluating Static Function Calls</h5><p>This section applies to static function calls where none of the arguments is an <code>ArgumentPlaceholder</code>. For function calls involving placeholders, see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p> When a static function call <var>FC</var> is evaluated with respect to a static context <var>SC</var> and a dynamic context <var>DC</var>, the result is obtained as follows: </p><ol class="enumar"><li><p> The <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> to be used is found in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a> of <var>SC</var>. </p><p>The <b>required arity</b> is the total number of arguments in the function call, including both positional and keyword arguments.</p><p> There can be at most one <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a> component of <var>SC</var> whose function name matches the expanded QName in <var>FC</var> and whose <a title="arity range" class="termref" href="#dt-arity-range">arity range</a> includes the arity of <var>FC</var>’s <code>ArgumentList</code>. </p><p>If there is no such <a title="function definition" class="termref" href="#dt-function-definition">function definition</a>, a static error [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>] is raised.</p></li><li><p>Each parameter in the <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> is matched to an argument expression as follows:</p><ol class="enumla"><li><p>If there are <var>N</var> positional arguments in the function call <var>FC</var>, then the corresponding argument expressions are matched pairwise to the first <var>N</var> parameters in the declaration. For this purpose the required parameters and optional parameters in <var>FD</var> are concatenated into a single list, in order.</p></li><li><p>Any keyword arguments in <var>FC</var> are then matched to parameters (whether required or optional) in <var>FD</var> by comparing the keyword used in <var>FC</var> with the paramater name declared in <var>FD</var>. Each keyword must match the name of a declared parameter [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>], and this must be one that has not already been matched to a positional argument. [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>].</p></li><li><p>If any required parameter has not been matched to any argument in <var>FC</var> by applying the above rules, a static error is reported [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>] </p></li><li><p>If any optional parameter has not been matched to any argument in <var>FC</var> by applying the above rules, then the parameter is matched to the default value expression for that parameter in <var>FD</var>.</p></li></ol></li><li><p> Each argument expression established by the above rules is evaluated with respect to DC. The order of argument evaluation is <a title="implementation   dependent" class="termref" href="#dt-implementation-dependent">implementation dependent</a> and it is not required that an argument be evaluated if the function body can be evaluated without evaluating that argument.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>All argument expressions, including default value expressions, are evaluated in the dynamic context of the function call. It is therefore possible to use a default value expression such as <code>.</code>, or <code>/</code>, or <code>fn:current-dateTime()</code>, whose value depends on the dynamic context of the function call.</p></div><p>If the expression used for the default value of a parameter has no dependencies on the dynamic context, then an implementation <span class="verb">may</span> choose to reuse the same value on repeated function calls rather than re-evaluating it on each function call.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>This is relevant, for example, if the expression constructs new nodes.</p></div></li><li><p>The result of evaluating the argument expression is converted to the required type (the declared type associated with the corresponding parameter in the function declaration, defaulting to <code>item()*</code>) by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>.</p><p><span>This applies both to explicitly supplied arguments, and to values obtained by evaluating default value expressions. In both cases a type error will be raised if the value (after coercion) does not match the required type.</span></p></li><li><p>The result of the function call is obtained as follows:</p><ul><li><p><var>FD</var>’s <span>body</span> is invoked in an implementation-dependent way. The processor makes the following information available to that invocation: </p><ul><li><p>The converted argument values;</p></li><li><p>If the function is <a title="context dependent" class="termref" href="#dt-context-dependent">context dependent</a>, the static context <var>SC</var> and dynamic context <var>DC</var> of the function call. </p></li></ul></li><li><p>The result is converted to the required type (the declared return type in the function declaration, defaulting to <code>item()*</code>) by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>.</p><p>The result of applying the coercion rules is either an instance of <var>FD</var>’s return type or a dynamic error. This result is then the result of evaluating <var>FC</var>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>A host language may define alternative rules for processing the result, especially in the case of external functions implemented using a non-XDM type system.</p></div></li><li><p> Errors raised by system functions are defined in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>. </p></li><li class="xpath"><p> Errors raised by host-language-dependent functions are <a title="implementation defined" class="termref" href="#dt-implementation-defined">implementation-defined</a>. </p></li></ul><div class="example"><div class="exampleHeader"><a id="d3e15861"></a>Example: A System Function</div><p>The following function call uses the function <a href="https://qt4cg.org/specifications/xpath-functions-40/#func-base-uri">Section 2.1.5 fn:base-uri</a><sup><small>FO</small></sup>. Use of <code>SC</code> and <code>DC</code> and errors raised by this function are all defined in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>.</p><div class="exampleInner"><pre xml:space="preserve">base-uri()</pre></div></div></li></ol></div></div><div class="div3"><h4><a id="id-dynamic-functions"></a>4.5.2 Function Items</h4><p>A <a title="function item" class="termref" href="#dt-function-item">function item</a> is an XDM value that can be bound to a variable, or manipulated in various ways by XPath 4.0 expressions. The most significant such expression is a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-call">dynamic function call</a>, which supplies values of arguments and evaluates the function to produce a result.</p><p>The syntax of dynamic function calls is defined in <a href="#id-dynamic-function-invocation"><b>4.5.2.1 Dynamic Function Calls</b></a>.</p><p>A number of constructs can be used to produce a <a title="function item" class="termref" href="#dt-function-item">function item</a>, notably:</p><ul><li><p>A <b>named function reference</b> (see <a href="#id-named-function-ref"><b>4.5.2.4 Named Function References</b></a>) constructs a function item by reference to <a title="function definition" class="termref" href="#dt-function-definition">function definitions</a> in the static context. For example, <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-node-name"><code>fn:node-name#1</code></a> returns a function item whose effect is to call the static <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-node-name"><code>fn:node-name</code></a> function with one argument.</p></li><li><p>An <b>inline function</b> (see <a href="#id-inline-func"><b>4.5.2.5 Inline Function Expressions</b></a> ) constructs a function item whose <span>body</span> is defined locally. For example, the construct <code>fn($x) { $x + 1 }</code> returns a function item whose effect is to increment the value of the supplied argument.</p></li><li><p>A <b>partial function application</b> (see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>) derives one function item from another by supplying the values of some of its arguments. For example, <code>fn:ends-with(?, ".txt")</code> returns a function item with one argument that tests whether the supplied string ends with the substring <code>".txt"</code>.</p></li><li><p>Maps and arrays are also function items. See <a href="#id-map-constructors"><b>4.13.1.1 Map Constructors</b></a> and <a href="#id-array-constructors"><b>4.13.2.1 Array Constructors</b></a>.</p></li><li><p>The <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-function-lookup"><code>fn:function-lookup</code></a> function can be called to discover functions that are present in the <a title="dynamic context" class="termref" href="#dt-dynamic-context">dynamic context</a>.</p></li><li><p>The <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-load-xquery-module"><code>fn:load-xquery-module</code></a> function can be called to load functions dynamically from an external XQuery library module.</p></li><li><p>Some system functions such as <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-random-number-generator"><code>fn:random-number-generator</code></a> and <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-op"><code>fn:op</code></a> return a <a title="function item" class="termref" href="#dt-function-item">function item</a> as their result.</p></li></ul><p>These constructs are described in detail in the following sections, or in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>.</p><div class="div4"><h5><a id="id-dynamic-function-invocation"></a>4.5.2.1 Dynamic Function Calls</h5><a id="d3e15970"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-DynamicFunctionCall"></a><code><a href="#prod-xpath40-DynamicFunctionCall">DynamicFunctionCall</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-PositionalArgumentList">PositionalArgumentList</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-PositionalArgumentList"></a><code><a href="#prod-xpath40-PositionalArgumentList">PositionalArgumentList</a></code></td><td>::=</td><td><code>"(" <a href="#doc-xpath40-PositionalArguments">PositionalArguments</a>? ")"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-PositionalArguments"></a><code><a href="#prod-xpath40-PositionalArguments">PositionalArguments</a></code></td><td>::=</td><td><code>(<a href="#doc-xpath40-Argument">Argument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e14809.doc-xpath40-Argument"></a><code>Argument</code></td><td>::=</td><td><code><a href="#doc-xpath40-ExprSingle">ExprSingle</a> | <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e14810.doc-xpath40-ArgumentPlaceholder"></a><code>ArgumentPlaceholder</code></td><td>::=</td><td><code>"?"</code></td></tr></tbody></table><p> [<a id="dt-dynamic-function-invocation" title="dynamic function call">Definition</a>: A <b>dynamic function call</b> consists of a base expression that returns the function and a parenthesized list of zero or more arguments (<a title="argument expression" class="termref" href="#dt-arg-expr">argument expressions</a> or ArgumentPlaceholders).] </p><p> A dynamic function call is evaluated as described in <a href="#id-eval-dynamic-function-call"><b>4.5.2.2 Evaluating Dynamic Function Calls</b></a>. </p><p>The following are examples of some dynamic function calls:</p><ul><li><p>This example calls the function contained in <code>$f</code>, passing the arguments 2 and 3: </p><div class="exampleInner"><pre xml:space="preserve">$f(2, 3)</pre></div></li><li><p>This example fetches the second item from sequence <code>$f</code>, treats it as a function and calls it, passing an <code>xs:string</code> argument: </p><div class="exampleInner"><pre xml:space="preserve">$f[2]("Hi there")</pre></div></li><li><p>This example calls the function <code>$f</code> passing no arguments, and filters the result with a positional predicate: </p><div class="exampleInner"><pre xml:space="preserve">$f()[2]</pre></div></li></ul><div class="note"><p class="prefix"><b>Note:</b></p><p>Arguments in a dynamic function call are always supplied positionally.</p></div></div><div class="div4"><h5><a id="id-eval-dynamic-function-call"></a>4.5.2.2 Evaluating Dynamic Function Calls</h5><p>This section applies to dynamic function calls whose arguments do not include an <code>ArgumentPlaceholder</code>. For function calls that include a placeholder, see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p> [<a id="dt-dynamic-function-call" title="dynamic function call">Definition</a>: A <b>dynamic function call</b> is an expression that is evaluated by calling a <a title="function item" class="termref" href="#dt-function-item">function item</a>, which is typically obtained dynamically.] </p><p> When a dynamic function call <var>FC</var> is evaluated, the result is obtained as follows: </p><ol class="enumar"><li><p> The <a title="function item" class="termref" href="#dt-function-item">function item</a><var>FI</var> to be called is obtained by evaluating the base expression of the function call. If this yields a sequence consisting of a single function item whose arity matches the number of arguments in the <code>ArgumentList</code>, let <var>FI</var> denote that function item. Otherwise, a type error is raised [<a href="#ERRXPTY0004" title="err:XPTY0004">err:XPTY0004</a>]. </p><div class="note"><p class="prefix"><b>Note:</b></p><p>Keyword arguments are not allowed in a dynamic function call.</p></div></li><li><p><a title="argument expression" class="termref" href="#dt-arg-expr">Argument expressions</a> are evaluated, producing <b>argument values</b>. The order of argument evaluation is <a title="implementation   dependent" class="termref" href="#dt-implementation-dependent">implementation-dependent</a> and an argument need not be evaluated if the function body can be evaluated without evaluating that argument.</p></li><li><p> Each argument value is converted to the corresponding parameter type in <var>FI</var>’s signature by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>, resulting in a <b>converted argument value</b></p></li><li><p>If <var>FI</var> is a map, it is evaluated as described in <a href="#id-map-lookup"><b>4.13.1.2 Maps as Functions</b></a>.</p></li><li><p>If <var>FI</var> is an array, it is evaluated as described in <a href="#id-array-lookup"><b>4.13.2.2 Arrays as Functions</b></a>.</p></li><li><p> If <var>FI</var>’s <span>body</span> is an XPath 4.0 expression (for example, if <var>FI</var> is an <a title="anonymous function" class="termref" href="#dt-anonymous-function">anonymous function</a>, or a <a title="partially applied function" class="termref" href="#dt-partially-applied-function">partial application</a> of such a function): </p><ol class="enumla"><li><p><var>FI</var>’s <span>body</span> is evaluated. The static context for this evaluation is the static context of the XPath 4.0 expression. The dynamic context for this evaluation is obtained by taking the dynamic context of the <span class="xpath"><code>InlineFunctionExpr</code></span> that contains the <code>FunctionBody</code>, and making the following changes: </p><ul><li><p> The <a title="focus" class="termref" href="#dt-focus">focus</a> (context value, context position, and context size) is <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#dt-absent">absent</a><sup><small>DM</small></sup>. </p></li><li><p> In the <a title="variable values" class="termref" href="#dt-variable-values">variable values</a> component of the dynamic context, each converted argument value is bound to the corresponding parameter name. </p><p><span>When this is done, the converted argument values retain their <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic types</a>, even where these are <a title="subtype" class="termref" href="#dt-subtype">subtypes</a> of the declared parameter types.</span> For example, a function with a parameter <code>$p</code> of type <code>xs:decimal</code> can be called with an argument of type <code>xs:integer</code>, which is derived from <code>xs:decimal</code>. During the processing of this function call, the value of <code>$p</code> inside the body of the function retains its <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic type</a> of <code>xs:integer</code>. </p></li><li><p><var>FI</var>’s nonlocal variable bindings are also added to the <a title="variable values" class="termref" href="#dt-variable-values">variable values</a>. (Note that the names of the nonlocal variables are by definition disjoint from the parameter names, so there can be no conflict.) </p></li></ul></li><li><p> The value returned by evaluating the function body is then converted to the declared return type of <var>FI</var> by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>. The result is then the result of evaluating <var>FC</var>. </p><p> As with argument values, the value returned by a function retains its <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic type</a>, which may be a <a title="subtype" class="termref" href="#dt-subtype">subtype</a> of the declared return type of <var>FI</var>. For example, a function that has a declared return type of <code>xs:decimal</code> may in fact return a value of dynamic type <code>xs:integer</code>. </p></li></ol><div class="example"><div class="exampleHeader"><a id="d3e16244"></a>Example: Derived Types and Nonlocal Variable Bindings</div><p><code>$incr</code> is a nonlocal variable that is available within the function because its variable binding has been added to the variable values of the function.. Even though the parameter and return type of this function are both <code>xs:decimal</code>, the more specific type <code>xs:integer</code> is preserved in both cases.</p><div class="exampleInner"><pre xml:space="preserve">let $incr := 1
+return local:filter(1 to 10, $f)</pre></div><p>Here the supplied function <code>$f</code> is an instance of the required type, because its signature defaults the argument type to <code>item()*</code>, which is a supertype of <code>xs:string</code>. The expression <code>$s[$p(.)]</code> could in principle succeed. However, function coercion ensures that the supplied function is wrapped in a function that requires the argument to be of type <code>xs:string</code>, so the call fails with a type error when the wrapping function is invoked supplying an <code>xs:integer</code> as the argument.</p></div></div><div class="div3"><h4><a id="id-coercion-examples"></a>3.4.5 Examples of Coercions</h4><p>This section illustrates the effect of the coercion rules with examples.</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-string"></a>Example: Coercion to <code>xs:string</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:string</code>. For example, the second argument of <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-matches"><code>fn:matches</code></a>, which expects a regular expression. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>"[0-9]"</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>default-language()</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of <code>xs:language</code>, which is a subtype of the required type <code>xs:string</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;[0-9]&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. Unless it has been schema-validated, the typed value will be an instance of <code>xs:untypedAtomic</code>, which is accepted when the required type is <code>xs:string</code>.</p><p>Supplying an element whose type annotation is (say) <code>xs:date</code> will fail with a type error.</p><p class="xpath">The effect is subtly different if XPath 1.0 compatibility mode is enabled. In this case coercion takes the string value of the element node. This differs from the typed value only in the case where the element has been schema-validated and has a type annotation other than <code>xs:string</code>.</p></td></tr><tr><td style="vertical-align:top"><code>xs:anyURI("urn:dummy")</code></td><td style="vertical-align:top"><p>Supplying an instance of <code>xs:anyURI</code> where the expected type is <code>xs:string</code> is permitted; this is one of the pairs of types where implicit casting is allowed.</p></td></tr><tr class="xpath"><td style="vertical-align:top"><code>17.2</code></td><td style="vertical-align:top"><p>Supplying a number where a string is expected raises a type error.</p><p class="xpath">However, if XPath 1.0 compatibility mode is enabled, the number is converted to a string as if by the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-string"><code>fn:string</code></a> function.</p></td></tr><tr class="xpath"><td style="vertical-align:top"><code>//author/@id</code></td><td style="vertical-align:top"><p>Supplying a sequence of nodes where a single string is expected will raise a type error unless either there is only one node in the sequence. In this case the typed value of the node will be used (this must be of type <code>xs:string</code>, <code>xs:untypedAtomic</code>, or <code>xs:anyURI</code>).</p><p class="xpath">If XPath 1.0 compatibility mode is enabled, however, all strings after the first are discarded, and the string value of the first node is used; if the sequence is empty, a zero-length string is supplied.</p></td></tr><tr class="xpath"><td style="vertical-align:top"><code>("red", "green", "blue")</code></td><td style="vertical-align:top"><p>Supplying a sequence of strings where a single string is expected raises a type error.</p><p class="xpath">If XPath 1.0 compatibility mode is enabled, however, all strings after the first are discarded; the effect is as if the supplied value were <code>"red"</code>.</p></td></tr><tr class="xpath"><td style="vertical-align:top"><code>()</code></td><td style="vertical-align:top"><p>Supplying an empty sequence where a single string is expected will fail.</p><p class="xpath">If XPath 1.0 compatibility mode is enabled, however, the value is coerced by applying the function <code>fn:string(())</code>, which delivers the zero-length string.</p></td></tr><tr><td style="vertical-align:top"><code>["a|b"]</code></td><td style="vertical-align:top"><p>Supplying an array holding a single string succeeds, because the rules cause the array to be atomized, and the value after atomization is a single string.</p><p>Supplying an array holding multiple strings would fail.</p><p class="xpath">In XPath 1.0 compatibility mode, supplying an array will fail, regardless of the array contents, because the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-string"><code>fn:string</code></a> function does not accept arrays.</p></td></tr></tbody></table></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-decimal"></a>Example: Coercion to <code>xs:decimal?</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:decimal?</code>. For example, the first argument of <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-seconds"><code>fn:seconds</code></a>, which expects a decimal number of seconds. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>12.4</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>()</code></td><td style="vertical-align:top"><p>None; an empty sequence is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>42</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of <code>xs:integer</code>, which is a subtype of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>math:pi()</code></td><td style="vertical-align:top"><p>The supplied value is an instance of <code>xs:double</code>, which can be converted to <code>xs:decimal</code> under the coercion rules.</p></td></tr><tr><td style="vertical-align:top"><code>("a", "b")[.="c"]</code></td><td style="vertical-align:top"><p>The supplied value is an empty sequence, which is a valid instance of the required type <code>xs:decimal?</code>. However, the processor may (optionally) reject this as an implausible coercion, on the grounds that it can only succeed in one special case, namely where the filter expression selects no values. </p></td></tr><tr><td style="vertical-align:top"><code>(1.5, 2.5, 3.5)</code></td><td style="vertical-align:top"><p>A type error is raised<span class="xpath">, except in the case where XPath 1.0 compatibility is enabled, in which case all values after the first are discarded</span>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;3.14159&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The element node is atomized; unless it has been schema-validated, the result will be <code>"3.14159"</code> as an instance of <code>xs:untypedAtomic</code>. This is converted to an instance of <code>xs:decimal</code> following the rules of the <code>cast as</code> operator.</p></td></tr><tr class="xpath"><td style="vertical-align:top"><code>"12.2"</code></td><td style="vertical-align:top"><p>Supplying a string where an <code>xs:decimal</code> is a type error<span class="xpath">, even if XPath 1.0 compatibility mode is enabled. The rules for compatibility mode would allow conversion if the required type were <code>xs:double</code>, but not for <code>xs:decimal</code></span>. </p></td></tr><tr><td style="vertical-align:top"><code>[1.5]</code></td><td style="vertical-align:top"><p>The array is atomized, and the result is a valid instance of the required type <code>xs:decimal?</code></p></td></tr><tr><td style="vertical-align:top"><code>[]</code></td><td style="vertical-align:top"><p>The array is atomized, and the result is an empty sequence, which is a valid instance of the required type <code>xs:decimal?</code></p></td></tr></tbody></table></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-positive-integer"></a>Example: Coercion to <code>xs:positive-integer</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:positive-integer</code>. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>12</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:integer</code>. Because the supplied value and the required type, <code>xs:positiveInteger</code>, both come under the primitive type <code>xs:decimal</code>, and the value <code>12</code> is within the value space of <code>xs:positiveInteger</code>, the value is relabeled as an <code>xs:positiveInteger</code> and the call succeeds.</p></td></tr><tr><td style="vertical-align:top"><code>12.1</code></td><td style="vertical-align:top"><p>This fails with a type error, because the <code>xs:decimal</code> value <code>12.1</code> is not a value in the value space of <code>xs:positiveInteger</code>. This is so even though casting to <code>xs:positiveInteger</code> would succeed.</p></td></tr><tr><td style="vertical-align:top"><code>math:pi()</code></td><td style="vertical-align:top"><p>This fails with a type error. A value of type <code>xs:double</code> is accepted where the required type is <code>xs:decimal</code> or <code>xs:float</code>, but not where it is <code>xs:positiveInteger</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;1200&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. If the element has not been schema-validated, the result will be an <code>xs:untypedAtomic</code> item, which is successfully cast to the required type <code>xs:positiveInteger</code>. If the element has been validated against a schema, then coercion succeeds if the typed value would itself be acceptable, for example if it is an <code>xs:positiveInteger</code>, or some other <code>xs:decimal</code> within the value space of <code>xs:positiveInteger</code>.</p></td></tr></tbody></table></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-union"></a>Example: Coercion to a union type</div><p>Consider the first parameter of the function <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a>, whose declared type is <code>(xs:string | xs:positiveInteger)</code>. The rules are the same as if it were a union typed declared in an imported schema.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>"amp"</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:string</code>, which is one of the allowed types. The call therefore succeeds.</p></td></tr><tr><td style="vertical-align:top"><code>"#"</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:string</code>, which is one of the allowed types. As far as the coercion rules are concerned, the call therefore succeeds. Under the semantic rules for the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a> function, however, this value is not accepted; a dynamic error (as distinct from a type error) is therefore raised.</p></td></tr><tr><td style="vertical-align:top"><code>0x25</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:integer</code>. Although this is not one of the allowed types, it is acceptable because coercion of the value to type <code>xs:positiveInteger</code> succeeds. The value is relabeled as an instance of <code>xs:positiveInteger</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;0x25&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. Assuming that the node has not been schema-validated, the result is an instance of <code>xs:untypedAtomic</code>. The member types of the choice are tested in order. Conversion to <code>xs:string</code> with the value "0x25" succeeds, so the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a> function is called supplying this string; but the function rejects this string as semantically invalid. The same would happen if the value were, say, &lt;a&gt;37&lt;/a&gt;. Supplying such a value requires an explicit cast, for example <code>fn:char( xs:positiveInteger( ./a ))</code>.</p></td></tr></tbody></table></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-choice"></a>Example: Coercion to a choice type</div><p>Suppose the required type is <code>(record(x as xs:decimal, y as xs:decimal, *) | record(size as enum("S", "M", "L", "XL"), *))</code>.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>{ "x": 1, "y": 2, "z": 3 }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of the first record type: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "size": "M" }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of the second record type: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1, "y": 2, "size": "XL" }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of both record types: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1e0, "y": 2e0, "size": "XL" }</code></td><td style="vertical-align:top"><p>The supplied value is not an instance of the first record type because the fields are of type <code>xs:double</code> rather than <code>xs:decimal</code>. It is however an instance of the second record type. It is therefore accepted <em>as is</em>; the fields <code>x</code> and <code>y</code> are not converted from <code>xs:double</code> to <code>xs:decimal</code>.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1e0, "y": 2e0, "size": "XXL" }</code></td><td style="vertical-align:top"><p>The supplied value is not an instance of the first record type because the fields are of type <code>xs:double</code> rather than <code>xs:decimal</code>, and it is not an instance of the second record type because the <code>size</code> value does not match the enumeration type. Coercion is therefore attempted to the first record type, and succeeds. The <code>x</code> and <code>y</code> fields are coerced to <code>xs:decimal</code>, and the <code>size</code> field is accepted <em>as is</em>.</p></td></tr></tbody></table></div></div></div><div class="div2"><h3><a id="id-predefined-types"></a>3.5 Schema Types</h3><p> [<a id="dt-schema-type" title="schema type">Definition</a>: A <b>schema type</b> is a complex type or simple type as defined in the <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> specifications, including built-in types as well as user-defined types.] </p><p>Every schema type is either a <b>complex type</b> or a <b>simple type</b>; simple types are further subdivided into <b>list types</b>, <b>union types</b>, and <b>atomic types</b> (see <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> for definitions and explanations of these terms.)</p><p>A schema type can appear as a type annotation on an element or attribute node. The type annotation on an element node can be a complex type or a simple type; the type annotation on an attribute node is always a simple type. Non-instantiable types such as <code>xs:NOTATION</code> or <code>xs:anyAtomicType</code> never appear as type annotations, but their derived types can be so used. Union types never appear as type annotations; when an element or attribute is validated against a union type, the resulting type annotation will be one of the types in the transitive membership of the union type.</p><p> [<a id="dt-atomic-type" title="atomic type">Definition</a>: An <b>atomic type</b> is a simple <a title="schema type" class="termref" href="#dt-schema-type">schema type</a> whose <a href="https://www.w3.org/TR/xmlschema11-1/#std-variety">{variety}<sup><small>XS11-1</small></sup></a> is <code>atomic</code>.] </p><p>An <b>atomic type</b> is either a built-in atomic type (defined either in the XSD specification or in this specification), or it is a user-defined atomic type included in an imported schema.</p><p class="xpath">The <a title="in-scope schema type" class="termref" href="#dt-is-types">in-scope schema types</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a> are initialized with a set of predefined schema types that is determined by the host language. This set may include some or all of the schema types in the namespace <code>http://www.w3.org/2001/XMLSchema</code>, represented in this document by the namespace prefix <code>xs</code>. The schema types in this namespace are defined in <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> and augmented by additional types defined in <a href="#xpath-datamodel-40">[XQuery and XPath Data Model (XDM) 4.0]</a>. An implementation that has based its type system on <a href="#XMLSchema10">[XML Schema 1.0]</a> is not required to support the <code>xs:dateTimeStamp</code> or <code>xs:error</code> types.</p><p>The schema types defined in <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#types-predefined">Section 2.8.3 Predefined Types</a><sup><small>DM</small></sup> are summarized below.</p><ol class="enumar"><li><p> [<a id="dt-untyped" title="xs:untyped">Definition</a>: <code>xs:untyped</code> is used as the <a title="type annotation" class="termref" href="#dt-type-annotation">type annotation</a> of an element node that has not been validated, or has been validated in <code>skip</code> mode.] No predefined schema types are derived from <code>xs:untyped</code>.</p></li><li><p> [<a id="dt-untypedAtomic" title="xs:untypedAtomic">Definition</a>: <code>xs:untypedAtomic</code> is an <a title="atomic type" class="termref" href="#dt-atomic-type">atomic type</a> that is used to denote untyped atomic data, such as text that has not been assigned a more specific type.] An attribute that has been validated in <code>skip</code> mode is represented in the <a title="data model" class="termref" href="#dt-datamodel">data model</a> by an attribute node with the <a title="type annotation" class="termref" href="#dt-type-annotation">type annotation</a><code>xs:untypedAtomic</code>. No predefined schema types are derived from <code>xs:untypedAtomic</code>.</p></li><li><p> [<a id="dt-dayTimeDuration" title="xs:dayTimeDuration">Definition</a>: <code>xs:dayTimeDuration</code> is derived by restriction from <code>xs:duration</code>. The lexical representation of <code>xs:dayTimeDuration</code> is restricted to contain only day, hour, minute, and second components.] </p></li><li><p> [<a id="dt-yearMonthDuration" title="xs:yearMonthDuration">Definition</a>: <code>xs:yearMonthDuration</code> is derived by restriction from <code>xs:duration</code>. The lexical representation of <code>xs:yearMonthDuration</code> is restricted to contain only year and month components.] </p></li><li><p> [<a id="dt-anyAtomicType" title="xs:anyAtomicType">Definition</a>: <code>xs:anyAtomicType</code> is an <a title="atomic type" class="termref" href="#dt-atomic-type">atomic type</a> that includes all atomic items (and no values that are not atomic). Its base type is <code>xs:anySimpleType</code> from which all simple types, including atomic, list, and union types, are derived. All primitive atomic types, such as <code>xs:decimal</code> and <code>xs:string</code>, have <code>xs:anyAtomicType</code> as their base type.] </p><div class="note"><p class="prefix"><b>Note:</b></p><p><code>xs:anyAtomicType</code> will not appear as the type of an actual value in an <a title="XDM instance" class="termref" href="#dt-data-model-instance">XDM instance</a>.</p></div></li><li><p> [<a id="dt-xs-error" title="xs:error">Definition</a>: <code>xs:error</code> is a simple type with no value space. It is defined in <a href="https://www.w3.org/TR/xmlschema11-1/#xsd-error">Section 3.16.7.3 xs:error </a><sup><small>XS11-1</small></sup> and can be used in the <a href="#id-sequencetype-syntax"><b>3.1 Sequence Types</b></a> to raise errors.] </p></li></ol><p>The relationships among the schema types in the <code>xs</code> namespace are illustrated in Figure 2. A more complete description of the XPath 4.0 type hierarchy can be found in <a href="https://qt4cg.org/specifications/xpath-functions-40/#datatypes">Section 1.8 Type System</a><sup><small>FO</small></sup>.</p><img src="types.jpg" alt="Type Hierarchy Diagram"><p>Figure 2: Hierarchy of Schema Types used in XPath 4.0.</p></div></div><div class="div1"><h2><a id="id-expressions"></a>4 Expressions</h2><p>This section discusses each of the basic kinds of expression. Each kind of expression has a name such as <code>PathExpr</code>, which is introduced on the left side of the grammar production that defines the expression. Since XPath 4.0 is a composable language, each kind of expression is defined in terms of other expressions whose operators have a higher precedence. In this way, the precedence of operators is represented explicitly in the grammar.</p><p>The order in which expressions are discussed in this document does not reflect the order of operator precedence. In general, this document introduces the simplest kinds of expressions first, followed by more complex expressions. For the complete grammar, see Appendix [<a href="#nt-bnf"><b>A XPath 4.0 Grammar</b></a>].</p><p><span class="xpath">The highest-level symbol in the XPath grammar is XPath.</span></p><a id="d3e13837"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-XPath"></a><code><a href="#prod-xpath40-XPath">XPath</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-Expr">Expr</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-Expr"></a><code><a href="#prod-xpath40-Expr">Expr</a></code></td><td>::=</td><td><code>(<a href="#doc-xpath40-ExprSingle">ExprSingle</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-ExprSingle"></a><code><a href="#prod-xpath40-ExprSingle">ExprSingle</a></code></td><td>::=</td><td><span style="display: none;" class="delete_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-OrExpr">OrExpr</a></code></span><span style="display: none;" class="add_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-PipelineExpr">PipelineExpr</a></code></span><span class="modify_version"><code><a href="#doc-xpath40-ForExpr">ForExpr</a><br>| <a href="#prod-xpath40-LetExpr">LetExpr</a><br>| <a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xpath40-IfExpr">IfExpr</a><br>| <a href="#doc-xpath40-OrExpr"><span class="deltaxml-old" style="background:#FF5555">OrExpr</span></a><a href="#doc-xpath40-PipelineExpr"><span class="deltaxml-new" style="background:#90EE90">PipelineExpr</span></a></code></span></td></tr></tbody></table><p>The XPath 4.0 operator that has lowest precedence is the <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a>, which is used to combine two operands to form a sequence. As shown in the grammar, a general expression (<a href="#doc-xpath40-Expr">Expr</a>) can consist of multiple <a href="#doc-xpath40-ExprSingle">ExprSingle</a> operands, separated by commas.</p><p>The name <a href="#doc-xpath40-ExprSingle">ExprSingle</a> denotes an expression that does not contain a top-level <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a> (despite its name, an <a href="#doc-xpath40-ExprSingle">ExprSingle</a> may evaluate to a sequence containing more than one item.)</p><p>The symbol <a href="#doc-xpath40-ExprSingle">ExprSingle</a> is used in various places in the grammar where an expression is not allowed to contain a top-level comma. For example, each of the arguments of a function call must be a <a href="#doc-xpath40-ExprSingle">ExprSingle</a>, because commas are used to separate the arguments of a function call.</p><p><span style="display: none;" class="delete_version">After the comma, the expressions that have next lowest precedence are <span class="xpath"><a href="#doc-xpath40-ForExpr">ForExpr</a>, <a href="#doc-xpath40-LetExpr">LetExpr</a>, </span><a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a>, <a href="#doc-xpath40-IfExpr">IfExpr</a>, and <a href="#doc-xpath40-OrExpr">OrExpr</a>. Each of these expressions is described in a separate section of this document.</span><span style="display: none;" class="add_version">After the comma, the expressions that have next lowest precedence are <span class="xpath"><a href="#doc-xpath40-ForExpr">ForExpr</a>, <a href="#doc-xpath40-LetExpr">LetExpr</a>, </span><a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a>, <a href="#doc-xpath40-IfExpr">IfExpr</a>, and <a href="#doc-xpath40-PipelineExpr">PipelineExpr</a>. Each of these expressions is described in a separate section of this document.</span><span class="modify_version">After the comma, the expressions that have next lowest precedence are <span class="xpath"><a href="#doc-xpath40-ForExpr">ForExpr</a>, <a href="#doc-xpath40-LetExpr">LetExpr</a>, </span><a href="#doc-xpath40-QuantifiedExpr">QuantifiedExpr</a>, <a href="#doc-xpath40-IfExpr">IfExpr</a>, and <a href="#doc-xpath40-OrExpr"><span class="deltaxml-old" style="background:#FF5555">OrExpr</span></a><a href="#doc-xpath40-PipelineExpr"><span class="deltaxml-new" style="background:#90EE90">PipelineExpr</span></a>. Each of these expressions is described in a separate section of this document.</span></p><div class="div2"><h3><a id="comments"></a>4.1 Comments</h3><a id="d3e13934"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-Comment"></a><code><a href="#prod-xpath40-Comment">Comment</a></code></td><td>::=</td><td><code>"(:" (<a href="#doc-xpath40-CommentContents">CommentContents</a> | <a href="#doc-xpath40-Comment">Comment</a>)* ":)"</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-comments">gn: comments</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-CommentContents"></a><code><a href="#prod-xpath40-CommentContents">CommentContents</a></code></td><td>::=</td><td><code>(<a href="#prod-xpath40-Char">Char</a>+ - (Char* ('(:' | ':)') Char*))</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>Comments may be used to provide information relevant to programmers who read <span class="xpath">an expression</span>. Comments are lexical constructs only, and do not affect <span class="xpath">expression</span> processing.</p><p>Comments are strings, delimited by the symbols <code>(:</code> and <code>:)</code>. Comments may be nested.</p><p>A comment may be used anywhere <a title="ignorable whitespace" class="termref" href="#IgnorableWhitespace">ignorable whitespace</a> is allowed (see <a href="#DefaultWhitespaceHandling"><b>A.3.5.1 Default Whitespace Handling</b></a>).</p><p>The following is an example of a comment:</p><div class="exampleInner"><pre xml:space="preserve">(: Houston, we have a problem :)</pre></div></div><div class="div2"><h3><a id="id-primary-expressions"></a>4.2 Primary Expressions</h3><p> [<a id="dt-primary-expression" title="primary expression">Definition</a>: <b>Primary expressions</b> are the basic primitives of the language. They include literals, variable references, context value references, and function calls. A primary expression may also be created by enclosing any expression in parentheses, which is sometimes helpful in controlling the precedence of operators.] Map and Array Constructors are described in <a href="#id-maps"><b>4.13.1 Maps</b></a> and <a href="#id-arrays"><b>4.13.2 Arrays</b></a>. </p><a id="d3e14008"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-PrimaryExpr"></a><code><a href="#prod-xpath40-PrimaryExpr">PrimaryExpr</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-Literal">Literal</a><br>| <a href="#doc-xpath40-VarRef">VarRef</a><br>| <a href="#doc-xpath40-ParenthesizedExpr">ParenthesizedExpr</a><br>| <a href="#doc-xpath40-ContextValueRef">ContextValueRef</a><br>| <a href="#doc-xpath40-FunctionCall">FunctionCall</a><br>| <a href="#doc-xpath40-FunctionItemExpr">FunctionItemExpr</a><br>| <a href="#doc-xpath40-MapConstructor">MapConstructor</a><br>| <a href="#doc-xpath40-ArrayConstructor">ArrayConstructor</a><br>| <a href="#doc-xpath40-StringTemplate">StringTemplate</a><br>| <a href="#doc-xpath40-UnaryLookup">UnaryLookup</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-FunctionItemExpr"></a><code><a href="#prod-xpath40-FunctionItemExpr">FunctionItemExpr</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-NamedFunctionRef">NamedFunctionRef</a> | <a href="#doc-xpath40-InlineFunctionExpr">InlineFunctionExpr</a></code></td></tr></tbody></table><div class="div3"><h4><a id="id-literals"></a>4.2.1 Literals</h4><a id="d3e14079"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-Literal"></a><code><a href="#prod-xpath40-Literal">Literal</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-NumericLiteral">NumericLiteral</a> | <a href="#doc-xpath40-StringLiteral">StringLiteral</a></code></td></tr></tbody></table><p> [<a id="dt-literal" title="literal">Definition</a>: A <b>literal</b> is a direct syntactic representation of an atomic item.] XPath 4.0 supports two kinds of literals: numeric literals and string literals.</p><div class="div4"><h5><a id="id-numeric-literals"></a>4.2.1.1 Numeric Literals</h5><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-filter-expression">⬇</a>&nbsp;<a href="#id-function-coercion">⬆</a></p><ol><li><p> Numeric literals can now be written in hexadecimal or binary notation; and underscores can be included for readability. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/429">429</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/433">433</a>&nbsp;25 April 2023]</i></p></li></ol></div><a id="d3e14105"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-NumericLiteral"></a><code><a href="#prod-xpath40-NumericLiteral">NumericLiteral</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-IntegerLiteral">IntegerLiteral</a> | <a href="#doc-xpath40-HexIntegerLiteral">HexIntegerLiteral</a> | <a href="#doc-xpath40-BinaryIntegerLiteral">BinaryIntegerLiteral</a> | <a href="#doc-xpath40-DecimalLiteral">DecimalLiteral</a> | <a href="#doc-xpath40-DoubleLiteral">DoubleLiteral</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-IntegerLiteral"></a><code><a href="#prod-xpath40-IntegerLiteral">IntegerLiteral</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-Digits">Digits</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-HexIntegerLiteral"></a><code><a href="#prod-xpath40-HexIntegerLiteral">HexIntegerLiteral</a></code></td><td>::=</td><td><code>"0x" <a href="#doc-xpath40-HexDigits">HexDigits</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-BinaryIntegerLiteral"></a><code><a href="#prod-xpath40-BinaryIntegerLiteral">BinaryIntegerLiteral</a></code></td><td>::=</td><td><code>"0b" <a href="#doc-xpath40-BinaryDigits">BinaryDigits</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-DecimalLiteral"></a><code><a href="#prod-xpath40-DecimalLiteral">DecimalLiteral</a></code></td><td>::=</td><td><code>("." <a href="#doc-xpath40-Digits">Digits</a>) | (<a href="#doc-xpath40-Digits">Digits</a> "." <a href="#doc-xpath40-Digits">Digits</a>?)</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-DoubleLiteral"></a><code><a href="#prod-xpath40-DoubleLiteral">DoubleLiteral</a></code></td><td>::=</td><td><code>(("." <a href="#doc-xpath40-Digits">Digits</a>) | (<a href="#doc-xpath40-Digits">Digits</a> ("." <a href="#doc-xpath40-Digits">Digits</a>?)?)) [eE] [+-]? <a href="#doc-xpath40-Digits">Digits</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-Digits"></a><code><a href="#prod-xpath40-Digits">Digits</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-DecDigit">DecDigit</a> ((<a href="#doc-xpath40-DecDigit">DecDigit</a> | "_")* <a href="#doc-xpath40-DecDigit">DecDigit</a>)?</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-DecDigit"></a><code><a href="#prod-xpath40-DecDigit">DecDigit</a></code></td><td>::=</td><td><code>[0-9]</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-HexDigits"></a><code><a href="#prod-xpath40-HexDigits">HexDigits</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-HexDigit">HexDigit</a> ((<a href="#doc-xpath40-HexDigit">HexDigit</a> | "_")* <a href="#doc-xpath40-HexDigit">HexDigit</a>)?</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-HexDigit"></a><code><a href="#prod-xpath40-HexDigit">HexDigit</a></code></td><td>::=</td><td><code>[0-9a-fA-F]</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-BinaryDigits"></a><code><a href="#prod-xpath40-BinaryDigits">BinaryDigits</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-BinaryDigit">BinaryDigit</a> ((<a href="#doc-xpath40-BinaryDigit">BinaryDigit</a> | "_")* <a href="#doc-xpath40-BinaryDigit">BinaryDigit</a>)?</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-BinaryDigit"></a><code><a href="#prod-xpath40-BinaryDigit">BinaryDigit</a></code></td><td>::=</td><td><code>[01]</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>The value of a numeric literal is determined as follows (taking the rules in order):</p><ol class="enumar"><li><p>Underscore characters are stripped out. Underscores may be included in a numeric literal to aid readability, but have no effect on the value. For example, <code>1_000_000</code> is equivalent to <code>1000000</code>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Underscores must not appear at the beginning or end of a sequence of digits, only in intermediate positions. Multiple adjacent underscores are allowed.</p></div></li><li><p>A <code>HexIntegerLiteral</code> represents a non-negative integer expressed in hexadecimal: for example <code>0xffff</code> represents the integer 65535, and <code>0xFFFF_FFFF</code> represents the integer 4294967295.</p></li><li><p>A <code>BinaryIntegerLiteral</code> represents a non-negative integer expressed in binary: for example <code>0b101</code> represents the integer 5, and <code>0b1111_1111</code> represents the integer 255.</p></li><li><p>The value of a <b>numeric literal</b> containing no <code>.</code> and no <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:integer</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:integer</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li><li><p>The value of a numeric literal containing <code>.</code> but no <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:decimal</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:decimal</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li><li><p>The value of a numeric literal containing an <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:double</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:double</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li></ol><div class="note"><p class="prefix"><b>Note:</b></p><p>The value of a numeric literal is always non-negative. An expression may appear to include a negative number such as <code>-1</code>, but this is technically an arithmetic expression comprising a unary minus operator followed by a numeric literal.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The effect of the above rules is that in the case of an integer or decimal literal, a dynamic error [<a href="https://qt4cg.org/specifications/xpath-functions-40/#ERRFOAR0002" title="err:FOAR0002">err:FOAR0002</a>]<sup><small>FO40</small></sup> will generally be raised if the literal is outside the range of values supported by the implementation (other options are available: see <a href="https://qt4cg.org/specifications/xpath-functions-40/#op.numeric">Section 4.2 Arithmetic operators on numeric values</a><sup><small>FO</small></sup> for details.)</p><p class="xpath">The XML Schema specification allows implementations to impose a limit (which must not be less than 18 digits) on the size of integer and decimal values. The full range of values of built-in subtypes of <code>xs:integer</code>, such as <code>xs:long</code> and <code>xs:unsignedLong</code>, can be supported only if the limit is 20 digits or higher. Negative numbers such as the minimum value of <code>xs:long</code> (<code>-9223372036854775808</code>) are technically unary expressions rather than literals, but implementations may prefer to ensure that they are expressible.</p></div><p>Here are some examples of numeric literals:</p><ul><li><p><code>12</code> denotes the <code>xs:integer</code> value twelve.</p></li><li><p><code>1_000_000</code> denotes the <code>xs:integer</code> value one million.</p></li><li><p><code>12.5</code> denotes the <code>xs:decimal</code> value twelve and one half.</p></li><li><p><code>3.14159_26535_89793e0</code> is an <code>xs:double</code> value representing the mathematical constant <var>π</var> to 15 decimal places. </p></li><li><p><code>125E2</code> denotes the <code>xs:double</code> value twelve thousand, five hundred.</p></li><li><p><code>0xffff</code> denotes the <code>xs:integer</code> value 65535.</p></li><li><p><code>0b1000_0001</code> denotes the <code>xs:integer</code> value 129.</p></li></ul></div><div class="div4"><h5><a id="id-string-literal"></a>4.2.1.2 String Literals</h5><a id="d3e14489"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-StringLiteral"></a><code><a href="#prod-xpath40-StringLiteral">StringLiteral</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-AposStringLiteral">AposStringLiteral</a> | <a href="#doc-xpath40-QuotStringLiteral">QuotStringLiteral</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-AposStringLiteral"></a><code><a href="#prod-xpath40-AposStringLiteral">AposStringLiteral</a></code></td><td>::=</td><td><code>"'" (<a href="#doc-xpath40-EscapeApos">EscapeApos</a> | [^'])* "'"</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-QuotStringLiteral"></a><code><a href="#prod-xpath40-QuotStringLiteral">QuotStringLiteral</a></code></td><td>::=</td><td><code>'"' (<a href="#doc-xpath40-EscapeQuot">EscapeQuot</a> | [^"])* '"'</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-EscapeQuot"></a><code><a href="#prod-xpath40-EscapeQuot">EscapeQuot</a></code></td><td>::=</td><td><code>'""'</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-EscapeApos"></a><code><a href="#prod-xpath40-EscapeApos">EscapeApos</a></code></td><td>::=</td><td><code>"''"</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>The value of a <b>string literal</b> is an atomic item whose type is <code>xs:string</code> and whose value is the string denoted by the characters between the delimiting apostrophes or quotation marks. If the literal is delimited by apostrophes, two adjacent apostrophes within the literal are interpreted as a single apostrophe. Similarly, if the literal is delimited by quotation marks, two adjacent quotation marks within the literal are interpreted as one quotation mark.</p><p>Here are some examples of string literals:</p><ul><li><p><code>"He said, ""I don't like it."""</code> denotes a string containing two quotation marks and one apostrophe.</p></li><li><p>In XQuery, the string literal <code>"&amp;lt;"</code> denotes a string of length 1 containing the single character <code>"&lt;"</code>. In XPath, the string literal <code>"&amp;lt;"</code> denotes a string of length 4 containing the four characters <code>"&amp;"</code>, <code>"l"</code>, <code>"t"</code>, <code>";"</code>. (However, when the XPath expression is embedded in an XML document, the sequence <code>"&amp;lt;"</code> will typically have already been converted to <code>"&lt;"</code> by the XML parser.)</p></li></ul><div class="note"><p class="prefix"><b>Note:</b></p><p>When XPath or XQuery expressions are embedded in contexts where quotation marks have special significance, such as inside XML attributes, or in string literals in a host language such as Java or C#, then additional escaping may be needed.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>Fixed string values can also be written as string templates: see <a href="#id-string-templates"><b>4.9.2 String Templates</b></a>. A string template with no enclosed expressions, such as <code>`Jamaica`</code> evaluates to the same value as the string literals <code>"Jamaica"</code> or <code>'Jamaica'</code>. A string template can contain both single and double quotation marks: <code>`He said: "I don't like it"`</code>. However, there there are some subtle differences:</p><ul><li><p>In string literals, the treatment of character and entity references such as <code>&amp;amp;</code> varies between XQuery and XPath; in string templates, such references are not expanded in either language.</p></li><li><p>String templates can only be used where an expression is expected. String literals are also used in some non-expression contexts, for example in defining an enumeration type: see <a href="#id-enumeration-types"><b>3.2.6 Enumeration Types</b></a>.</p></li><li><p>Curly brackets (<span class="unicode-codepoint">U+007B</span> (<span class="unicode-name">LEFT CURLY BRACKET</span>, <code>{</code>) and <span class="unicode-codepoint">U+007D</span> (<span class="unicode-name">RIGHT CURLY BRACKET</span>, <code>}</code>) ) and backticks (<span class="unicode-codepoint">U+0060</span> (<span class="unicode-name">GRAVE ACCENT, BACKTICK</span>, <code>`</code>) ) have a reserved meaning in string templates.</p></li></ul></div></div><div class="div4"><h5><a id="id-constants-other-types"></a>4.2.1.3 Constants of Other Types</h5><p> The <code>xs:boolean</code> values <code>true</code> and <code>false</code> can be constructed by calls to the <a title="system function" class="termref" href="#dt-system-function">system functions</a><code>fn:true()</code> and <code>fn:false()</code>, respectively. </p><p>Values of other simple types can be constructed by calling the <a title="constructor function" class="termref" href="#dt-constructor-function">constructor function</a> for the given type. The constructor functions for XML Schema built-in types are defined in <a href="https://qt4cg.org/specifications/xpath-functions-40/#constructor-functions-for-xsd-types">Section 20.1 Constructor functions for XML Schema built-in atomic types</a><sup><small>FO</small></sup>. In general, the name of a constructor function for a given type is the same as the name of the type (including its namespace). For example:</p><ul><li><p><code>xs:integer("12")</code> returns the integer value twelve.</p></li><li><p><code>xs:date("2001-08-25")</code> returns an item whose type is <code>xs:date</code> and whose value represents the date 25th August 2001.</p></li><li><p><code>xs:dayTimeDuration("PT5H")</code> returns an item whose type is <code>xs:dayTimeDuration</code> and whose value represents a duration of five hours.</p></li></ul><p>Constructor functions can also be used to create special values that have no literal representation, as in the following examples: </p><ul><li><p><code>xs:float("NaN")</code> returns the special floating-point value, "Not a Number."</p></li><li><p><code>xs:double("INF")</code> returns the special double-precision value, "positive infinity."</p></li></ul><p>Constructor functions are available for all simple types, including union types. For example, if <code>my:dt</code> is a user-defined union type whose member types are <code>xs:date</code>, <code>xs:time</code>, and <code>xs:dateTime</code>, then the expression <code>my:dt("2011-01-10")</code> creates an atomic item of type <code>xs:date</code>. The rules follow XML Schema validation rules for union types: the effect is to choose the first member type that accepts the given string in its lexical space.</p><p>It is also possible to construct values of various types by using a <code>cast</code> expression. For example:</p><ul><li><p><code>9 cast as hatsize</code> returns the atomic item <code>9</code> whose type is <code>hatsize</code>.</p></li></ul></div></div><div class="div3"><h4><a id="id-variables"></a>4.2.2 Variable References</h4><a id="d3e14744"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-VarRef"></a><code><a href="#prod-xpath40-VarRef">VarRef</a></code></td><td>::=</td><td><code>"$" <a href="#doc-xpath40-EQName">EQName</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e13737.doc-xpath40-EQName"></a><code>EQName</code></td><td>::=</td><td><code><a href="#doc-xpath40-QName">QName</a> | <a href="#doc-xpath40-URIQualifiedName">URIQualifiedName</a></code></td></tr></tbody></table><p> [<a id="dt-variable-reference" title="variable reference">Definition</a>: A <b>variable reference</b> is an EQName preceded by a $-sign.] An unprefixed variable reference is in no namespace. Two variable references are equivalent if their <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QNames</a> are equal (as defined by the <code>eq</code> operator). The scope of a variable binding is defined separately for each kind of expression that can bind variables.</p><p>Every variable reference must match a name in the <a title="in-scope variables" class="termref" href="#dt-in-scope-variables">in-scope variables</a>. </p><p>Every variable binding has a static scope. The scope defines where references to the variable can validly occur. It is a <a title="static error" class="termref" href="#dt-static-error">static error</a> [<a href="#ERRXPST0008" title="err:XPST0008">err:XPST0008</a>] to reference a variable that is not in scope. If a variable is bound in the <a title="static context" class="termref" href="#dt-static-context">static context</a> for an expression, that variable is in scope for the entire expression except where it is occluded by another binding that uses the same name within that scope.</p><p> At evaluation time, the value of a variable reference is the value to which the relevant variable is bound.</p></div><div class="div3"><h4><a id="id-context-value-references"></a>4.2.3 Context Value References</h4><a id="d3e14795"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-ContextValueRef"></a><code><a href="#prod-xpath40-ContextValueRef">ContextValueRef</a></code></td><td>::=</td><td><code>"."</code></td></tr></tbody></table><p>A <b>context value reference</b> evaluates to the <a title="context value" class="termref" href="#dt-context-value">context value</a>.</p><p>In many syntactic contexts, the context value will be a single item. For example this applies on the right-hand side of the <code>/</code> or <code>!</code> operators, or within a <a href="#doc-xpath40-Predicate">Predicate</a>.</p><p>If the <a title="context value" class="termref" href="#dt-context-value">context value</a> is <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#dt-absent">absent</a><sup><small>DM</small></sup>, a context value reference raises a <a title="type error" class="termref" href="#dt-type-error">type error</a> [<a href="#ERRXPDY0002" title="err:XPDY0002">err:XPDY0002</a>].</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Being absent is not the same thing as being empty.</p></div></div><div class="div3"><h4><a id="id-paren-expressions"></a>4.2.4 Parenthesized Expressions</h4><a id="d3e14831"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-ParenthesizedExpr"></a><code><a href="#prod-xpath40-ParenthesizedExpr">ParenthesizedExpr</a></code></td><td>::=</td><td><code>"(" <a href="#doc-xpath40-Expr">Expr</a>? ")"</code></td></tr></tbody></table><p>Parentheses may be used to override the precedence rules. For example, the expression <code>(2 + 4) * 5</code> evaluates to thirty, since the parenthesized expression <code>(2 + 4)</code> is evaluated first and its result is multiplied by five. Without parentheses, the expression <code>2 + 4 * 5</code> evaluates to twenty-two, because the multiplication operator has higher precedence than the addition operator.</p><p>Empty parentheses are used to denote an empty sequence, as described in <a href="#construct_seq"><b>4.7.1 Sequence Concatenation</b></a>.</p></div><div class="div3"><h4><a id="id-enclosed-expr"></a>4.2.5 Enclosed Expressions</h4><p><a id="d3e14859"></a></p><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-EnclosedExpr"></a><code><a href="#prod-xpath40-EnclosedExpr">EnclosedExpr</a></code></td><td>::=</td><td><code>"{" <a href="#doc-xpath40-Expr">Expr</a>? "}"</code></td></tr></tbody></table><p> [<a id="dt-enclosed-expression" title="enclosed expression">Definition</a>: An <b>enclosed expression</b> is an instance of the <a href="#doc-xpath40-EnclosedExpr">EnclosedExpr</a> production, which allows an optional expression within curly brackets.] [<a id="dt-content-expression" title="content expression">Definition</a>: In an <a title="enclosed expression" class="termref" href="#dt-enclosed-expression">enclosed expression</a>, the optional expression enclosed in curly brackets is called the <b>content expression</b>.] If the <a title="content expression" class="termref" href="#dt-content-expression">content expression</a> is not provided explicitly, the content expression is <code>()</code>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Despite the name, an enclosed expression is not actually an expression in its own right; rather it is a construct that is used in the grammar of many other expressions.</p></div></div></div><div class="div2"><h3><a id="id-postfix-expression"></a>4.3 Postfix Expressions</h3><a id="d3e14895"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-PostfixExpr"></a><code><a href="#prod-xpath40-PostfixExpr">PostfixExpr</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-PrimaryExpr">PrimaryExpr</a> | <a href="#doc-xpath40-FilterExpr">FilterExpr</a> | <a href="#doc-xpath40-DynamicFunctionCall">DynamicFunctionCall</a> | <a href="#doc-xpath40-LookupExpr">LookupExpr</a> | <a href="#doc-xpath40-FilterExprAM">FilterExprAM</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e13859.doc-xpath40-FilterExpr"></a><code>FilterExpr</code></td><td>::=</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Predicate">Predicate</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e13860.doc-xpath40-DynamicFunctionCall"></a><code>DynamicFunctionCall</code></td><td>::=</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-PositionalArgumentList">PositionalArgumentList</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e13861.doc-xpath40-LookupExpr"></a><code>LookupExpr</code></td><td>::=</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Lookup">Lookup</a></code></td></tr></tbody></table><p>A postfix expression takes one of the following forms:</p><ul><li><p> [<a id="dt-filter-expression" title="filter expression">Definition</a>: A <b>filter expression</b> is an expression in the form <code>E1[E2]</code>: its effect is to return those items from the value of <code>E1</code> that satisfy the predicate in E2.] </p><p>Filter expressions are described in <a href="#id-filter-expression"><b>4.4 Filter Expressions</b></a>.</p><p>An example of a filter expression is <code>(1 to 100)[. mod 2 = 0]</code> which returns all even numbers in the range 1 to 100.</p><p>The base expression <code>E1</code> can itself be a postfix expression, so multiple predicates are allowed, in the form <code>E1[E2][E3][E4]</code>.</p></li><li><p>An expression (other than a raw EQName) followed by an argument list in parentheses (that is, <code>E1(E2, E3, ...)</code>) is referred to as a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-invocation">dynamic function call</a>. Its effect is to evaluate <code>E1</code> to obtain a function, and then call that function, with <code>E2</code>, <code>E3</code>, <code>...</code> as arguments. Dynamic function calls are described in <a href="#id-dynamic-function-invocation"><b>4.5.2.1 Dynamic Function Calls</b></a>.</p><p>An example of a dynamic function call is <code>$f("a", 2)</code> where the value of variable <code>$f</code> must be a function item.</p></li><li><p>A <code>lookup-expression</code> takes the form <code>E1?K</code>, where <code>E1</code> is an expression returning a sequence of maps or arrays, and <code>K</code> is a key specifier, which indicates which entries in a map, or members in an array, should be selected.</p><p>Lookup expressions are described in <a href="#id-postfix-lookup"><b>4.13.3.1 Postfix Lookup Expressions</b></a>.</p><p>An example of a lookup expression is <code>$emp?name</code>, where the value of variable <code>$emp</code> is a map, and the string <code>"name"</code> is the key of one of the entries in the map.</p></li></ul><p>Postfix expressions are evaluated from left-to-right. For example, the expression <code>$E1[E2]?(E3)(E4)</code> is evaluated by first evaluating the filter expression <code>$E1[E2]</code> to produce a sequence of maps and arrays (say <code>$S</code>), then evaluating the lookup expression <code>$S?(E3)</code> to produce a function item (say <code>$F</code>), then evaluating the dynamic function call <code>$F(E4)</code> to produce the final result.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>The grammar for postfix expressions is defined here in a way designed to link clearly to the semantics of the different kinds of expression. For parsing purposes, the equivalent production rule:</p><div class="exampleInner"><pre xml:space="preserve">PostfixExpr := PrimaryExpr (Predicate | PositionalArgumentList | Lookup)*</pre></div><p>(as used in XPath 3.1) is probably more convenient.</p></div></div><div class="div2"><h3><a id="id-filter-expression"></a>4.4 Filter Expressions</h3><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-function-calls">⬇</a>&nbsp;<a href="#id-numeric-literals">⬆</a></p><ol><li><p> The value of a predicate in a filter expression can now be a sequence of integers. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/816">816</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/996">996</a>&nbsp;6 February 2024]</i></p></li></ol></div><a id="d3e15074"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-FilterExpr"></a><code><a href="#prod-xpath40-FilterExpr">FilterExpr</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-Predicate">Predicate</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-Predicate"></a><code><a href="#prod-xpath40-Predicate">Predicate</a></code></td><td>::=</td><td><code>"[" <a href="#doc-xpath40-Expr">Expr</a> "]"</code></td></tr></tbody></table><p>A filter expression consists of a base expression followed by a predicate, which is an expression written in square brackets. The result of the filter expression consists of the items returned by the base expression, filtered by applying the predicate to each item in turn. The ordering of the items returned by a filter expression is the same as their order in the result of the primary expression.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Where the expression before the square brackets is a <a href="#doc-xpath40-ReverseStep">ReverseStep</a> or <a href="#doc-xpath40-ForwardStep">ForwardStep</a>, the expression is technically not a filter expression but an <a href="#doc-xpath40-AxisStep">AxisStep</a>. There are minor differences in the semantics: see <a href="#id-predicate"><b>4.6.5 Predicates within Steps</b></a></p></div><p>Here are some examples of filter expressions:</p><ul><li><p>Given a sequence of products in a variable, return only those products whose price is greater than 100.</p><div class="exampleInner"><pre xml:space="preserve">$products[price gt 100]</pre></div></li><li><p>List all the integers from 1 to 100 that are divisible by 5. (See <a href="#construct_seq"><b>4.7.1 Sequence Concatenation</b></a> for an explanation of the <code>to</code> operator.)</p><div class="exampleInner"><pre xml:space="preserve">(1 to 100)[. mod 5 eq 0]</pre></div></li><li><p>The result of the following expression is the integer 25:</p><div class="exampleInner"><pre xml:space="preserve">(21 to 29)[5]</pre></div></li><li><p>The following example returns the fifth through ninth items in the sequence bound to variable <code>$orders</code>.</p><div class="exampleInner"><pre xml:space="preserve">$orders[5 to 9]</pre></div></li><li><p>The following example illustrates the use of a filter expression as a <a title="step" class="termref" href="#dt-step">step</a> in a <a title="path expression" class="termref" href="#dt-path-expression">path expression</a>. It returns the last chapter or appendix within the book bound to variable <code>$book</code>:</p><div class="exampleInner"><pre xml:space="preserve">$book/(chapter | appendix)[last()]</pre></div></li></ul><p>For each item in the input sequence, the predicate expression is evaluated using an <b>inner focus</b>, defined as follows: The context value is the item currently being tested against the predicate. The context size is the number of items in the input sequence. The context position is the position of the context value within the input sequence. </p><p>For each item in the input sequence, the result of the predicate expression is coerced to an <code>xs:boolean</code> value, called the <a title="predicate truth value" class="termref" href="#dt-predicate-truth-value">predicate truth value</a>, as described below. Those items for which the predicate truth value is <code>true</code> are retained, and those for which the predicate truth value is <code>false</code> are discarded.</p><p> [<a id="dt-predicate-truth-value" title="predicate truth value">Definition</a>: The <b>predicate truth value</b> of a value <code>$V</code> is the result of the expression <code>if ($V instance of xs:numeric+) then ($V = position()) else fn:boolean($V)</code>.] </p><p>Expanding this definition, the predicate truth value can be obtained by applying the following rules, in order:</p><ol class="enumar"><li><p>If the value <var>V</var> of the predicate expression is a sequence whose first item is an instance of the type <code>xs:numeric</code>, then:</p><ol class="enumla"><li><p><var>V</var> must be an instance of the type <code>xs:numeric+</code> (that is, every item in <var>V</var> must be numeric). A type error [<a href="https://qt4cg.org/specifications/xpath-functions-40/#ERRFORG0006" title="err:FORG0006">err:FORG0006</a>]<sup><small>FO40</small></sup> is raised if this is not the case.</p></li><li><p>The predicate truth value is <code>true</code> if <var>V</var> is equal (by the <code>=</code> operator) to the <b>context position</b>, and is <code>false</code> otherwise.</p></li></ol><p>In effect this means that an item in the input sequence is selected if its position in the sequence is equal to one or more of the numeric values in the predicate. For example, the predicate <code>[3 to 5]</code> is true for the third, fourth, and fifth items in the input sequence.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>It is possible, though not generally useful, for the value of a numeric predicate to depend on the focus, and thus to differ for different items in the input sequence. For example, the predicate <code>[xs:integer(@seq)]</code> selects those items in the input sequence whose <code>@seq</code> attribute is numerically equal to their position in the input sequence.</p><p>It is also possible, and again not generally useful, for the value of the predicate to be numeric for some items in the input sequence, and boolean for others. For example, the predicate <code>[@special otherwise last()]</code> is true for an item that either has an <code>@special</code> attribute, or is the last item in the input sequence.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The truth value of a numeric predicate does not depend on the order of the numbers in <var>V</var>. The predicates <code>[ 1, 2, 3 ]</code> and <code>[ 3, 2, 1 ]</code> have exactly the same effect. The items in the result of a filter expression always retain the ordering of the input sequence.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The truth value of a numeric predicate whose value is non-integral or non-positive is always false.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>Beware that using boolean operators (<code>and</code>, <code>or</code>, <code>not()</code>) with numeric values may not have the intended effect. For example the predicate <code>[1 or last()]</code> selects every item in the sequence, because <code>or</code> operates on the <a title="effective boolean value" class="termref" href="#dt-ebv">effective boolean value</a> of its operands. The required effect can be achieved with the predicate <code>[1, last()]</code>.</p></div></li><li><p>Otherwise, the predicate truth value is the <a title="effective boolean value" class="termref" href="#dt-ebv">effective boolean value</a> of the predicate expression.</p></li></ol></div><div class="div2"><h3><a id="id-functions"></a>4.5 Functions</h3><p>Functions in XPath 4.0 arise in two ways:</p><ul><li><p>A <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> contains information about a family of functions with the same name and a defined arity range. These functions are in most cases known statically (they appear in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a>), but there may be further function definitions that are known only dynamically (appearing in the <a title="dynamically known function definitions" class="termref" href="#dt-dynamically-known-function-definitions">dynamically known function definitions</a>).</p></li><li><p><a title="function item" class="termref" href="#dt-function-item">Function items</a> are XDM items that can be called using a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-call">dynamic function call</a>. They are values that can be bound to variables, passed as arguments, returned as function results, and generally manipulated in the same way as other XDM values.</p></li></ul><p>The functions defined by a statically known <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> can be invoked using a <a title="static function call" class="termref" href="#dt-static-function-call">static function call</a>. <a title="function item" class="termref" href="#dt-function-item">Function items</a> corresponding to these definitions can also be obtained, as dynamic values, by evaluating a <a title="named function reference" class="termref" href="#dt-named-function-ref">named function reference</a>. <a title="function item" class="termref" href="#dt-function-item">Function items</a> can also be obtained using the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-function-lookup"><code>fn:function-lookup</code></a> function: in this case the function name and arity do not need to be known statically, and the function definition need not be present in the <a title="static context" class="termref" href="#dt-static-context">static context</a>, so long as it is in the <a title="dynamic context" class="termref" href="#dt-dynamic-context">dynamic context</a>.</p><p>Static and dynamic function calls are described in the following sections.</p><div class="div3"><h4><a id="id-static-functions"></a>4.5.1 Static Function Calls</h4><p>The <a title="static context" class="termref" href="#dt-static-context">static context</a> for an expression includes a set of <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a>. Every <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context has a name (which is an <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a>) and an <a title="arity range" class="termref" href="#dt-arity-range">arity range</a>, which is a range of permitted arities for calls on that function. Two <a title="function definition" class="termref" href="#dt-function-definition">function definitions</a> having the same name must not have overlapping arity ranges. This means that for a given static function call, it is possible to identify the target function definition in the static context unambiguously from knowledge of the function name and the number of supplied arguments.</p><p>A <a title="static function call" class="termref" href="#dt-static-function-call">static function call</a> is bound to a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context by matching the name and arity. If the function call has <var>P</var> positional arguments followed by <var>K</var> keyword arguments, then the required arity is <var>P+K</var>, and the static context must include a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> whose name matches the <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a> in the function call, and whose <a title="arity range" class="termref" href="#dt-arity-range">arity range</a> includes this required arity. This is the function chosen to be called. The result of the function is obtained by evaluating the expression that forms its implementation, with a dynamic context that provides values for all the declared parameters, initialized as described in <a href="#id-eval-static-function-call"><b>4.5.1.2 Evaluating Static Function Calls</b></a> below.</p><p>Similarly, a function reference of the form <code>f#N</code> binds to a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context whose name matches <var>f</var> where <code>MinP ≤ N and MaxP ≥ N</code>. The result of evaluating a function reference is a <a title="function item" class="termref" href="#dt-function-item">function item</a> which can be called using a dynamic function call. Function items are never variadic and their arguments are always supplied positionally. For example, the function reference <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-concat"><code>fn:concat#3</code></a> returns a function item with arity 3, which is always called by supplying three positional arguments, and whose effect is the same as a static call on <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-concat"><code>fn:concat</code></a> with three positional arguments. </p><p>The detailed rules for evaluating static function calls and function references are defined in subsequent sections.</p><div class="div4"><h5><a id="id-function-calls"></a>4.5.1.1 Static Function Call Syntax</h5><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-inline-func">⬇</a>&nbsp;<a href="#id-filter-expression">⬆</a></p><ol><li><p> Keyword arguments are allowed on static function calls, as well as positional arguments. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/155">155</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/159">159</a>&nbsp;30 September 2020]</i></p></li></ol></div><a id="d3e15398"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-FunctionCall"></a><code><a href="#prod-xpath40-FunctionCall">FunctionCall</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-EQName">EQName</a><a href="#doc-xpath40-ArgumentList">ArgumentList</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-reserved-function-names">xgc: reserved-function-names</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-parens">gn: parens</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-ArgumentList"></a><code><a href="#prod-xpath40-ArgumentList">ArgumentList</a></code></td><td>::=</td><td><code>"(" ((<a href="#doc-xpath40-PositionalArguments">PositionalArguments</a> ("," <a href="#prod-xpath40-KeywordArguments">KeywordArguments</a>)?) | <a href="#prod-xpath40-KeywordArguments">KeywordArguments</a>)? ")"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e14299.doc-xpath40-PositionalArguments"></a><code>PositionalArguments</code></td><td>::=</td><td><code>(<a href="#doc-xpath40-Argument">Argument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-Argument"></a><code><a href="#prod-xpath40-Argument">Argument</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-ExprSingle">ExprSingle</a> | <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-ArgumentPlaceholder"></a><code><a href="#prod-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td><td>::=</td><td><code>"?"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e14302.doc-xpath40-KeywordArguments"></a><code>KeywordArguments</code></td><td>::=</td><td><code>(<a href="#doc-xpath40-KeywordArgument">KeywordArgument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-KeywordArgument"></a><code><a href="#prod-xpath40-KeywordArgument">KeywordArgument</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-EQName">EQName</a> ":=" <a href="#doc-xpath40-Argument">Argument</a></code></td></tr></tbody></table><p> [<a id="dt-static-function-call" title="static function call">Definition</a>: A <b>static function call</b> consists of an EQName followed by a parenthesized list of zero or more arguments.] </p><p>The argument list consists of zero or more positional arguments, followed by zero or more keyword arguments.</p><p> [<a id="dt-arg-expr" title="argument expression">Definition</a>: An argument to a function call is either an <b>argument expression</b> or an <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a> (<code>?</code>); in both cases it may either be supplied positionally, or identified by a name (called a keyword).] </p><p>This section is concerned with static function calls in which none of the arguments are <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholders</a>. Calls using one or more <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholders</a> are covered in the section <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p>If the function name supplied in a static function call is an unprefixed <a title="lexical QName" class="termref" href="#dt-qname">lexical QName</a>, it is expanded using the <a title="default function namespace" class="termref" href="#dt-default-function-namespace">default function namespace</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a>. </p><p> The <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a> used as the function name and the number of arguments used in the static function call (the required arity) must match the name and arity range of a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a><span> using the rules defined in the previous section</span>; if there is no match, a <a title="static error" class="termref" href="#dt-static-error">static error</a> is raised [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>]. </p><p>Evaluation of static function calls is described in <a href="#id-eval-static-function-call"><b>4.5.1.2 Evaluating Static Function Calls</b></a> .</p><p>Since the arguments of a function call are separated by commas, any <a title="argument expression" class="termref" href="#dt-arg-expr">argument expression</a> that contains a top-level <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a> must be enclosed in parentheses. Here are some illustrative examples of static function calls:</p><ul><li><p><code>my:three-argument-function(1, 2, 3)</code> denotes a static function call with three <span>positional</span> arguments. <span>The corresponding function declaration must define at least three parameters, and may define more, provided they are optional.</span></p></li><li><p><code>my:two-argument-function((1, 2), 3)</code> denotes a static function call with two arguments, the first of which is a sequence of two values. <span>The corresponding function declaration must define at least two parameters, and may define more, provided they are optional.</span></p></li><li><p><code>my:two-argument-function(1, ())</code> denotes a static function call with two arguments, the second of which is an empty sequence.</p></li><li><p><code>my:one-argument-function((1, 2, 3))</code> denotes a static function call with one argument that is a sequence of three values. </p></li><li><p><code>my:one-argument-function(( ))</code> denotes a static function call with one argument that is an empty sequence.</p></li><li><p><code>my:zero-argument-function( )</code> denotes a static function call with zero arguments.</p></li><li><p><code>lang(node := $n, language := 'de')</code> is a static function call with two keyword arguments. The corresponding function declaration defines two parameters, a required parameter <code>language</code> and an optional parameter <code>node</code>. This call supplies values for both parameters. It is equivalent to the call <code>fn:lang('de', $n)</code>. Note that the keyword arguments are in a different order from the parameter declarations. </p></li><li><p><code>sort(//employee, key := fn($e) { xs:decimal($e/salary) })</code> is a static function call with one positional argument and one keyword argument. The corresponding function declaration defines three parameters, a required parameter <code>$input</code>, an optional parameter <code>$collation</code>, and an optional parameter <code>$key</code> This call supplies values for the first and third parameters, leaving the second parameter (<code>$collation</code>) to take its default value. The default value of the <code>$collation</code> parameter is given as <code>fn:default-collation()</code>, so the value supplied to the function is the default collation from the dynamic context of the caller. It is equivalent to the call <code>fn:sort(//employee, fn:default-collation(), fn($e) { xs:decimal($e/salary) })</code>. </p></li></ul><p>An <code>EQName</code> in a <code>KeywordArgument</code> is expanded to a QName value; if there is no prefix, then the name is in no namespace (otherwise the prefix is resolved in the usual way). The keywords used in a function call (after expansion to QNames) must be distinct [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>]; [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>].</p></div><div class="div4"><h5><a id="id-eval-static-function-call"></a>4.5.1.2 Evaluating Static Function Calls</h5><p>This section applies to static function calls where none of the arguments is an <code>ArgumentPlaceholder</code>. For function calls involving placeholders, see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p> When a static function call <var>FC</var> is evaluated with respect to a static context <var>SC</var> and a dynamic context <var>DC</var>, the result is obtained as follows: </p><ol class="enumar"><li><p> The <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> to be used is found in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a> of <var>SC</var>. </p><p>The <b>required arity</b> is the total number of arguments in the function call, including both positional and keyword arguments.</p><p> There can be at most one <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a> component of <var>SC</var> whose function name matches the expanded QName in <var>FC</var> and whose <a title="arity range" class="termref" href="#dt-arity-range">arity range</a> includes the arity of <var>FC</var>’s <code>ArgumentList</code>. </p><p>If there is no such <a title="function definition" class="termref" href="#dt-function-definition">function definition</a>, a static error [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>] is raised.</p></li><li><p>Each parameter in the <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> is matched to an argument expression as follows:</p><ol class="enumla"><li><p>If there are <var>N</var> positional arguments in the function call <var>FC</var>, then the corresponding argument expressions are matched pairwise to the first <var>N</var> parameters in the declaration. For this purpose the required parameters and optional parameters in <var>FD</var> are concatenated into a single list, in order.</p></li><li><p>Any keyword arguments in <var>FC</var> are then matched to parameters (whether required or optional) in <var>FD</var> by comparing the keyword used in <var>FC</var> with the paramater name declared in <var>FD</var>. Each keyword must match the name of a declared parameter [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>], and this must be one that has not already been matched to a positional argument. [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>].</p></li><li><p>If any required parameter has not been matched to any argument in <var>FC</var> by applying the above rules, a static error is reported [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>] </p></li><li><p>If any optional parameter has not been matched to any argument in <var>FC</var> by applying the above rules, then the parameter is matched to the default value expression for that parameter in <var>FD</var>.</p></li></ol></li><li><p> Each argument expression established by the above rules is evaluated with respect to DC. The order of argument evaluation is <a title="implementation   dependent" class="termref" href="#dt-implementation-dependent">implementation dependent</a> and it is not required that an argument be evaluated if the function body can be evaluated without evaluating that argument.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>All argument expressions, including default value expressions, are evaluated in the dynamic context of the function call. It is therefore possible to use a default value expression such as <code>.</code>, or <code>/</code>, or <code>fn:current-dateTime()</code>, whose value depends on the dynamic context of the function call.</p></div><p>If the expression used for the default value of a parameter has no dependencies on the dynamic context, then an implementation <span class="verb">may</span> choose to reuse the same value on repeated function calls rather than re-evaluating it on each function call.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>This is relevant, for example, if the expression constructs new nodes.</p></div></li><li><p>The result of evaluating the argument expression is converted to the required type (the declared type associated with the corresponding parameter in the function declaration, defaulting to <code>item()*</code>) by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>.</p><p><span>This applies both to explicitly supplied arguments, and to values obtained by evaluating default value expressions. In both cases a type error will be raised if the value (after coercion) does not match the required type.</span></p></li><li><p>The result of the function call is obtained as follows:</p><ul><li><p><var>FD</var>’s <span>body</span> is invoked in an implementation-dependent way. The processor makes the following information available to that invocation: </p><ul><li><p>The converted argument values;</p></li><li><p>If the function is <a title="context dependent" class="termref" href="#dt-context-dependent">context dependent</a>, the static context <var>SC</var> and dynamic context <var>DC</var> of the function call. </p></li></ul></li><li><p>The result is converted to the required type (the declared return type in the function declaration, defaulting to <code>item()*</code>) by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>.</p><p>The result of applying the coercion rules is either an instance of <var>FD</var>’s return type or a dynamic error. This result is then the result of evaluating <var>FC</var>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>A host language may define alternative rules for processing the result, especially in the case of external functions implemented using a non-XDM type system.</p></div></li><li><p> Errors raised by system functions are defined in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>. </p></li><li class="xpath"><p> Errors raised by host-language-dependent functions are <a title="implementation defined" class="termref" href="#dt-implementation-defined">implementation-defined</a>. </p></li></ul><div class="example"><div class="exampleHeader"><a id="d3e15861"></a>Example: A System Function</div><p>The following function call uses the function <a href="https://qt4cg.org/specifications/xpath-functions-40/#func-base-uri">Section 2.1.5 fn:base-uri</a><sup><small>FO</small></sup>. Use of <code>SC</code> and <code>DC</code> and errors raised by this function are all defined in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>.</p><div class="exampleInner"><pre xml:space="preserve">base-uri()</pre></div></div></li></ol></div></div><div class="div3"><h4><a id="id-dynamic-functions"></a>4.5.2 Function Items</h4><p>A <a title="function item" class="termref" href="#dt-function-item">function item</a> is an XDM value that can be bound to a variable, or manipulated in various ways by XPath 4.0 expressions. The most significant such expression is a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-call">dynamic function call</a>, which supplies values of arguments and evaluates the function to produce a result.</p><p>The syntax of dynamic function calls is defined in <a href="#id-dynamic-function-invocation"><b>4.5.2.1 Dynamic Function Calls</b></a>.</p><p>A number of constructs can be used to produce a <a title="function item" class="termref" href="#dt-function-item">function item</a>, notably:</p><ul><li><p>A <b>named function reference</b> (see <a href="#id-named-function-ref"><b>4.5.2.4 Named Function References</b></a>) constructs a function item by reference to <a title="function definition" class="termref" href="#dt-function-definition">function definitions</a> in the static context. For example, <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-node-name"><code>fn:node-name#1</code></a> returns a function item whose effect is to call the static <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-node-name"><code>fn:node-name</code></a> function with one argument.</p></li><li><p>An <b>inline function</b> (see <a href="#id-inline-func"><b>4.5.2.5 Inline Function Expressions</b></a> ) constructs a function item whose <span>body</span> is defined locally. For example, the construct <code>fn($x) { $x + 1 }</code> returns a function item whose effect is to increment the value of the supplied argument.</p></li><li><p>A <b>partial function application</b> (see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>) derives one function item from another by supplying the values of some of its arguments. For example, <code>fn:ends-with(?, ".txt")</code> returns a function item with one argument that tests whether the supplied string ends with the substring <code>".txt"</code>.</p></li><li><p>Maps and arrays are also function items. See <a href="#id-map-constructors"><b>4.13.1.1 Map Constructors</b></a> and <a href="#id-array-constructors"><b>4.13.2.1 Array Constructors</b></a>.</p></li><li><p>The <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-function-lookup"><code>fn:function-lookup</code></a> function can be called to discover functions that are present in the <a title="dynamic context" class="termref" href="#dt-dynamic-context">dynamic context</a>.</p></li><li><p>The <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-load-xquery-module"><code>fn:load-xquery-module</code></a> function can be called to load functions dynamically from an external XQuery library module.</p></li><li><p>Some system functions such as <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-random-number-generator"><code>fn:random-number-generator</code></a> and <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-op"><code>fn:op</code></a> return a <a title="function item" class="termref" href="#dt-function-item">function item</a> as their result.</p></li></ul><p>These constructs are described in detail in the following sections, or in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>.</p><div class="div4"><h5><a id="id-dynamic-function-invocation"></a>4.5.2.1 Dynamic Function Calls</h5><a id="d3e15970"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-DynamicFunctionCall"></a><code><a href="#prod-xpath40-DynamicFunctionCall">DynamicFunctionCall</a></code></td><td>::=</td><td><code><a href="#doc-xpath40-PostfixExpr">PostfixExpr</a><a href="#doc-xpath40-PositionalArgumentList">PositionalArgumentList</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-PositionalArgumentList"></a><code><a href="#prod-xpath40-PositionalArgumentList">PositionalArgumentList</a></code></td><td>::=</td><td><code>"(" <a href="#doc-xpath40-PositionalArguments">PositionalArguments</a>? ")"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-PositionalArguments"></a><code><a href="#prod-xpath40-PositionalArguments">PositionalArguments</a></code></td><td>::=</td><td><code>(<a href="#doc-xpath40-Argument">Argument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e14809.doc-xpath40-Argument"></a><code>Argument</code></td><td>::=</td><td><code><a href="#doc-xpath40-ExprSingle">ExprSingle</a> | <a href="#doc-xpath40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e14810.doc-xpath40-ArgumentPlaceholder"></a><code>ArgumentPlaceholder</code></td><td>::=</td><td><code>"?"</code></td></tr></tbody></table><p> [<a id="dt-dynamic-function-invocation" title="dynamic function call">Definition</a>: A <b>dynamic function call</b> consists of a base expression that returns the function and a parenthesized list of zero or more arguments (<a title="argument expression" class="termref" href="#dt-arg-expr">argument expressions</a> or ArgumentPlaceholders).] </p><p> A dynamic function call is evaluated as described in <a href="#id-eval-dynamic-function-call"><b>4.5.2.2 Evaluating Dynamic Function Calls</b></a>. </p><p>The following are examples of some dynamic function calls:</p><ul><li><p>This example calls the function contained in <code>$f</code>, passing the arguments 2 and 3: </p><div class="exampleInner"><pre xml:space="preserve">$f(2, 3)</pre></div></li><li><p>This example fetches the second item from sequence <code>$f</code>, treats it as a function and calls it, passing an <code>xs:string</code> argument: </p><div class="exampleInner"><pre xml:space="preserve">$f[2]("Hi there")</pre></div></li><li><p>This example calls the function <code>$f</code> passing no arguments, and filters the result with a positional predicate: </p><div class="exampleInner"><pre xml:space="preserve">$f()[2]</pre></div></li></ul><div class="note"><p class="prefix"><b>Note:</b></p><p>Arguments in a dynamic function call are always supplied positionally.</p></div></div><div class="div4"><h5><a id="id-eval-dynamic-function-call"></a>4.5.2.2 Evaluating Dynamic Function Calls</h5><p>This section applies to dynamic function calls whose arguments do not include an <code>ArgumentPlaceholder</code>. For function calls that include a placeholder, see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p> [<a id="dt-dynamic-function-call" title="dynamic function call">Definition</a>: A <b>dynamic function call</b> is an expression that is evaluated by calling a <a title="function item" class="termref" href="#dt-function-item">function item</a>, which is typically obtained dynamically.] </p><p> When a dynamic function call <var>FC</var> is evaluated, the result is obtained as follows: </p><ol class="enumar"><li><p> The <a title="function item" class="termref" href="#dt-function-item">function item</a><var>FI</var> to be called is obtained by evaluating the base expression of the function call. If this yields a sequence consisting of a single function item whose arity matches the number of arguments in the <code>ArgumentList</code>, let <var>FI</var> denote that function item. Otherwise, a type error is raised [<a href="#ERRXPTY0004" title="err:XPTY0004">err:XPTY0004</a>]. </p><div class="note"><p class="prefix"><b>Note:</b></p><p>Keyword arguments are not allowed in a dynamic function call.</p></div></li><li><p><a title="argument expression" class="termref" href="#dt-arg-expr">Argument expressions</a> are evaluated, producing <b>argument values</b>. The order of argument evaluation is <a title="implementation   dependent" class="termref" href="#dt-implementation-dependent">implementation-dependent</a> and an argument need not be evaluated if the function body can be evaluated without evaluating that argument.</p></li><li><p> Each argument value is converted to the corresponding parameter type in <var>FI</var>’s signature by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>, resulting in a <b>converted argument value</b></p></li><li><p>If <var>FI</var> is a map, it is evaluated as described in <a href="#id-map-lookup"><b>4.13.1.2 Maps as Functions</b></a>.</p></li><li><p>If <var>FI</var> is an array, it is evaluated as described in <a href="#id-array-lookup"><b>4.13.2.2 Arrays as Functions</b></a>.</p></li><li><p> If <var>FI</var>’s <span>body</span> is an XPath 4.0 expression (for example, if <var>FI</var> is an <a title="anonymous function" class="termref" href="#dt-anonymous-function">anonymous function</a>, or a <a title="partially applied function" class="termref" href="#dt-partially-applied-function">partial application</a> of such a function): </p><ol class="enumla"><li><p><var>FI</var>’s <span>body</span> is evaluated. The static context for this evaluation is the static context of the XPath 4.0 expression. The dynamic context for this evaluation is obtained by taking the dynamic context of the <span class="xpath"><code>InlineFunctionExpr</code></span> that contains the <code>FunctionBody</code>, and making the following changes: </p><ul><li><p> The <a title="focus" class="termref" href="#dt-focus">focus</a> (context value, context position, and context size) is <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#dt-absent">absent</a><sup><small>DM</small></sup>. </p></li><li><p> In the <a title="variable values" class="termref" href="#dt-variable-values">variable values</a> component of the dynamic context, each converted argument value is bound to the corresponding parameter name. </p><p><span>When this is done, the converted argument values retain their <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic types</a>, even where these are <a title="subtype" class="termref" href="#dt-subtype">subtypes</a> of the declared parameter types.</span> For example, a function with a parameter <code>$p</code> of type <code>xs:decimal</code> can be called with an argument of type <code>xs:integer</code>, which is derived from <code>xs:decimal</code>. During the processing of this function call, the value of <code>$p</code> inside the body of the function retains its <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic type</a> of <code>xs:integer</code>. </p></li><li><p><var>FI</var>’s nonlocal variable bindings are also added to the <a title="variable values" class="termref" href="#dt-variable-values">variable values</a>. (Note that the names of the nonlocal variables are by definition disjoint from the parameter names, so there can be no conflict.) </p></li></ul></li><li><p> The value returned by evaluating the function body is then converted to the declared return type of <var>FI</var> by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>. The result is then the result of evaluating <var>FC</var>. </p><p> As with argument values, the value returned by a function retains its <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic type</a>, which may be a <a title="subtype" class="termref" href="#dt-subtype">subtype</a> of the declared return type of <var>FI</var>. For example, a function that has a declared return type of <code>xs:decimal</code> may in fact return a value of dynamic type <code>xs:integer</code>. </p></li></ol><div class="example"><div class="exampleHeader"><a id="d3e16244"></a>Example: Derived Types and Nonlocal Variable Bindings</div><p><code>$incr</code> is a nonlocal variable that is available within the function because its variable binding has been added to the variable values of the function.. Even though the parameter and return type of this function are both <code>xs:decimal</code>, the more specific type <code>xs:integer</code> is preserved in both cases.</p><div class="exampleInner"><pre xml:space="preserve">let $incr := 1
 let $f := function($i as xs:decimal) as xs:decimal { $i + $incr }
 return $f(5)</pre></div></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="d3e16259"></a>Example: Using the Context Value in an Anonymous Function</div><p>The following example will raise a <a title="type error" class="termref" href="#dt-type-error">type error</a> [<a href="#ERRXPDY0002" title="err:XPDY0002">err:XPDY0002</a>]:</p><div class="exampleInner"><pre xml:space="preserve">let $vat := function() { @vat + @price }
 return doc('wares.xml')/shop/article/$vat()</pre></div><p>Instead, the context value can be used as an argument to the anonymous function:</p><div class="exampleInner"><pre xml:space="preserve">let $vat := function($art) { $art/@vat + $art/@price }
diff --git a/pr/1686/xquery-40/xpath-40-diff.html b/pr/1686/xquery-40/xpath-40-diff.html
index 12ecbda87..8b7dbbbde 100644
--- a/pr/1686/xquery-40/xpath-40-diff.html
+++ b/pr/1686/xquery-40/xpath-40-diff.html
@@ -8804,7 +8804,7 @@ <h2><a id="id-expressions"></a>4 Expressions</h2>
 
          <a href="#doc-xpath40-IfExpr">IfExpr</a>,
 
-and <a href="#doc-xpath40-OrExpr">OrExpr</a>. Each of these expressions is described in a separate section of this document.</p>
+and <a href="#doc-xpath40-PipelineExpr">PipelineExpr</a>. Each of these expressions is described in a separate section of this document.</p>
             <div class="div2">
                
                <h3><a id="comments"></a>4.1 Comments</h3>
diff --git a/pr/1686/xquery-40/xpath-40.html b/pr/1686/xquery-40/xpath-40.html
index cf7c744f6..6f055119b 100644
--- a/pr/1686/xquery-40/xpath-40.html
+++ b/pr/1686/xquery-40/xpath-40.html
@@ -8592,7 +8592,7 @@ <h2><a id="id-expressions"></a>4 Expressions</h2>
 
          <a href="#doc-xpath40-IfExpr">IfExpr</a>,
 
-and <a href="#doc-xpath40-OrExpr">OrExpr</a>. Each of these expressions is described in a separate section of this document.</p>
+and <a href="#doc-xpath40-PipelineExpr">PipelineExpr</a>. Each of these expressions is described in a separate section of this document.</p>
             <div class="div2">
                
                <h3><a id="comments"></a>4.1 Comments</h3>
diff --git a/pr/1686/xquery-40/xpath-40.xml b/pr/1686/xquery-40/xpath-40.xml
index 681fd59c3..08d4c7132 100644
--- a/pr/1686/xquery-40/xpath-40.xml
+++ b/pr/1686/xquery-40/xpath-40.xml
@@ -4035,7 +4035,7 @@ return local:filter(1 to 10, $f)</pre></div><p>Here the supplied function <code>
 
          <a href="#doc-xpath40-IfExpr">IfExpr</a>,
 
-and <a href="#doc-xpath40-OrExpr">OrExpr</a>. Each of these expressions is described in a separate section of this document.</p><div class="div2">
+and <a href="#doc-xpath40-PipelineExpr">PipelineExpr</a>. Each of these expressions is described in a separate section of this document.</p><div class="div2">
 <h3><a id="comments"/>4.1 Comments</h3>
 <a id="d3e13934"/><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xpath40-Comment"/><code><a href="#prod-xpath40-Comment">Comment</a></code></td><td>::=</td><td><code>"(:"  (<a href="#doc-xpath40-CommentContents">CommentContents</a>  |  <a href="#doc-xpath40-Comment">Comment</a>)*  ":)"</code></td></tr><tr><td/><td/><td style="text-align: right;" class="prodComment">/* 
                      <a href="#ws-explicit">ws: explicit</a>
diff --git a/pr/1686/xquery-40/xquery-40-autodiff.html b/pr/1686/xquery-40/xquery-40-autodiff.html
index 126d3bf6e..dd415a826 100644
--- a/pr/1686/xquery-40/xquery-40-autodiff.html
+++ b/pr/1686/xquery-40/xquery-40-autodiff.html
@@ -96,7 +96,7 @@
 
 let $f := function($a) { $a mod 2 = 0 }
 return local:filter(1 to 10, $f)</pre></div><p>Here the supplied function <code>$f</code> is an instance of the required type, because its signature defaults the argument type to <code>item()*</code>, which is a supertype of <code>xs:string</code>. The expression <code>$s[$p(.)]</code> could in principle succeed. However, function coercion ensures that the supplied function is wrapped in a function that requires the argument to be of type <code>xs:string</code>, so the call fails with a type error when the wrapping function is invoked supplying an <code>xs:integer</code> as the argument.</p><p class="xquery">This has the consequence that in XQuery 4.0, there is a backwards incompatibility introduced because coercion rules now apply to global variable declarations (<code>declare variable</code>) and local variable bindings (for example <code>let</code> clauses). Previously the following would execute without error:</p><div class="exampleInner"><pre xml:space="preserve">let $f as function(xs:integer) as item()* := function($x) { $x + 1 }
-return $f(12.3)</pre></div><p class="xquery">With XQuery 4.0, as a consequence of function coercion, this fails with a type error because the argument supplied in the function call is not of type <code>xs:integer</code>.</p></div></div><div class="div3"><h4><a id="id-coercion-examples"></a>3.4.4 Examples of Coercions</h4><p>This section illustrates the effect of the coercion rules with examples.</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-string"></a>Example: Coercion to <code>xs:string</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:string</code>. For example, the second argument of <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-matches"><code>fn:matches</code></a>, which expects a regular expression. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>"[0-9]"</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>default-language()</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of <code>xs:language</code>, which is a subtype of the required type <code>xs:string</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;[0-9]&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. Unless it has been schema-validated, the typed value will be an instance of <code>xs:untypedAtomic</code>, which is accepted when the required type is <code>xs:string</code>.</p><p>Supplying an element whose type annotation is (say) <code>xs:date</code> will fail with a type error.</p></td></tr><tr><td style="vertical-align:top"><code>xs:anyURI("urn:dummy")</code></td><td style="vertical-align:top"><p>Supplying an instance of <code>xs:anyURI</code> where the expected type is <code>xs:string</code> is permitted; this is one of the pairs of types where implicit casting is allowed.</p></td></tr><tr><td style="vertical-align:top"><code>["a|b"]</code></td><td style="vertical-align:top"><p>Supplying an array holding a single string succeeds, because the rules cause the array to be atomized, and the value after atomization is a single string.</p><p>Supplying an array holding multiple strings would fail.</p></td></tr></tbody></table></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-decimal"></a>Example: Coercion to <code>xs:decimal?</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:decimal?</code>. For example, the first argument of <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-seconds"><code>fn:seconds</code></a>, which expects a decimal number of seconds. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>12.4</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>()</code></td><td style="vertical-align:top"><p>None; an empty sequence is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>42</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of <code>xs:integer</code>, which is a subtype of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>math:pi()</code></td><td style="vertical-align:top"><p>The supplied value is an instance of <code>xs:double</code>, which can be converted to <code>xs:decimal</code> under the coercion rules.</p></td></tr><tr><td style="vertical-align:top"><code>("a", "b")[.="c"]</code></td><td style="vertical-align:top"><p>The supplied value is an empty sequence, which is a valid instance of the required type <code>xs:decimal?</code>. However, the processor may (optionally) reject this as an implausible coercion, on the grounds that it can only succeed in one special case, namely where the filter expression selects no values. </p></td></tr><tr><td style="vertical-align:top"><code>(1.5, 2.5, 3.5)</code></td><td style="vertical-align:top"><p>A type error is raised.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;3.14159&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The element node is atomized; unless it has been schema-validated, the result will be <code>"3.14159"</code> as an instance of <code>xs:untypedAtomic</code>. This is converted to an instance of <code>xs:decimal</code> following the rules of the <code>cast as</code> operator.</p></td></tr><tr><td style="vertical-align:top"><code>[1.5]</code></td><td style="vertical-align:top"><p>The array is atomized, and the result is a valid instance of the required type <code>xs:decimal?</code></p></td></tr><tr><td style="vertical-align:top"><code>[]</code></td><td style="vertical-align:top"><p>The array is atomized, and the result is an empty sequence, which is a valid instance of the required type <code>xs:decimal?</code></p></td></tr></tbody></table></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-positive-integer"></a>Example: Coercion to <code>xs:positive-integer</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:positive-integer</code>. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>12</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:integer</code>. Because the supplied value and the required type, <code>xs:positiveInteger</code>, both come under the primitive type <code>xs:decimal</code>, and the value <code>12</code> is within the value space of <code>xs:positiveInteger</code>, the value is relabeled as an <code>xs:positiveInteger</code> and the call succeeds.</p></td></tr><tr><td style="vertical-align:top"><code>12.1</code></td><td style="vertical-align:top"><p>This fails with a type error, because the <code>xs:decimal</code> value <code>12.1</code> is not a value in the value space of <code>xs:positiveInteger</code>. This is so even though casting to <code>xs:positiveInteger</code> would succeed.</p></td></tr><tr><td style="vertical-align:top"><code>math:pi()</code></td><td style="vertical-align:top"><p>This fails with a type error. A value of type <code>xs:double</code> is accepted where the required type is <code>xs:decimal</code> or <code>xs:float</code>, but not where it is <code>xs:positiveInteger</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;1200&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. If the element has not been schema-validated, the result will be an <code>xs:untypedAtomic</code> item, which is successfully cast to the required type <code>xs:positiveInteger</code>. If the element has been validated against a schema, then coercion succeeds if the typed value would itself be acceptable, for example if it is an <code>xs:positiveInteger</code>, or some other <code>xs:decimal</code> within the value space of <code>xs:positiveInteger</code>.</p></td></tr></tbody></table></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-union"></a>Example: Coercion to a union type</div><p>Consider the first parameter of the function <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a>, whose declared type is <code>(xs:string | xs:positiveInteger)</code>. The rules are the same as if it were a union typed declared in an imported schema.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>"amp"</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:string</code>, which is one of the allowed types. The call therefore succeeds.</p></td></tr><tr><td style="vertical-align:top"><code>"#"</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:string</code>, which is one of the allowed types. As far as the coercion rules are concerned, the call therefore succeeds. Under the semantic rules for the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a> function, however, this value is not accepted; a dynamic error (as distinct from a type error) is therefore raised.</p></td></tr><tr><td style="vertical-align:top"><code>0x25</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:integer</code>. Although this is not one of the allowed types, it is acceptable because coercion of the value to type <code>xs:positiveInteger</code> succeeds. The value is relabeled as an instance of <code>xs:positiveInteger</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;0x25&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. Assuming that the node has not been schema-validated, the result is an instance of <code>xs:untypedAtomic</code>. The member types of the choice are tested in order. Conversion to <code>xs:string</code> with the value "0x25" succeeds, so the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a> function is called supplying this string; but the function rejects this string as semantically invalid. The same would happen if the value were, say, &lt;a&gt;37&lt;/a&gt;. Supplying such a value requires an explicit cast, for example <code>fn:char( xs:positiveInteger( ./a ))</code>.</p></td></tr></tbody></table></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-choice"></a>Example: Coercion to a choice type</div><p>Suppose the required type is <code>(record(x as xs:decimal, y as xs:decimal, *) | record(size as enum("S", "M", "L", "XL"), *))</code>.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>{ "x": 1, "y": 2, "z": 3 }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of the first record type: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "size": "M" }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of the second record type: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1, "y": 2, "size": "XL" }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of both record types: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1e0, "y": 2e0, "size": "XL" }</code></td><td style="vertical-align:top"><p>The supplied value is not an instance of the first record type because the fields are of type <code>xs:double</code> rather than <code>xs:decimal</code>. It is however an instance of the second record type. It is therefore accepted <em>as is</em>; the fields <code>x</code> and <code>y</code> are not converted from <code>xs:double</code> to <code>xs:decimal</code>.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1e0, "y": 2e0, "size": "XXL" }</code></td><td style="vertical-align:top"><p>The supplied value is not an instance of the first record type because the fields are of type <code>xs:double</code> rather than <code>xs:decimal</code>, and it is not an instance of the second record type because the <code>size</code> value does not match the enumeration type. Coercion is therefore attempted to the first record type, and succeeds. The <code>x</code> and <code>y</code> fields are coerced to <code>xs:decimal</code>, and the <code>size</code> field is accepted <em>as is</em>.</p></td></tr></tbody></table></div></div></div><div class="div2"><h3><a id="id-predefined-types"></a>3.5 Schema Types</h3><p> [<a id="dt-schema-type" title="schema type">Definition</a>: A <b>schema type</b> is a complex type or simple type as defined in the <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> specifications, including built-in types as well as user-defined types.] </p><p>Every schema type is either a <b>complex type</b> or a <b>simple type</b>; simple types are further subdivided into <b>list types</b>, <b>union types</b>, and <b>atomic types</b> (see <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> for definitions and explanations of these terms.)</p><p>A schema type can appear as a type annotation on an element or attribute node. The type annotation on an element node can be a complex type or a simple type; the type annotation on an attribute node is always a simple type. Non-instantiable types such as <code>xs:NOTATION</code> or <code>xs:anyAtomicType</code> never appear as type annotations, but their derived types can be so used. Union types never appear as type annotations; when an element or attribute is validated against a union type, the resulting type annotation will be one of the types in the transitive membership of the union type.</p><p> [<a id="dt-atomic-type" title="atomic type">Definition</a>: An <b>atomic type</b> is a simple <a title="schema type" class="termref" href="#dt-schema-type">schema type</a> whose <a href="https://www.w3.org/TR/xmlschema11-1/#std-variety">{variety}<sup><small>XS11-1</small></sup></a> is <code>atomic</code>.] </p><p>An <b>atomic type</b> is either a built-in atomic type (defined either in the XSD specification or in this specification), or it is a user-defined atomic type included in an imported schema.</p><p>The schema types defined in <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#types-predefined">Section 2.8.3 Predefined Types</a><sup><small>DM</small></sup> are summarized below.</p><p class="xquery">The <a title="in-scope schema type" class="termref" href="#dt-is-types">in-scope schema types</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a> are initialized with certain predefined schema types, including the built-in schema types in the namespace <code>http://www.w3.org/2001/XMLSchema</code>, which has the predefined namespace prefix <code>xs</code>. The schema types in this namespace are defined in <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> and augmented by additional types defined in <a href="#xpath-datamodel-40">[XQuery and XPath Data Model (XDM) 4.0]</a>. Element and attribute declarations in the <code>xs</code> namespace are not implicitly included in the static context. The schema types defined in <a href="#xpath-datamodel-40">[XQuery and XPath Data Model (XDM) 4.0]</a> are summarized below.</p><ol class="enumar"><li><p> [<a id="dt-untyped" title="xs:untyped">Definition</a>: <code>xs:untyped</code> is used as the <a title="type annotation" class="termref" href="#dt-type-annotation">type annotation</a> of an element node that has not been validated, or has been validated in <code>skip</code> mode.] No predefined schema types are derived from <code>xs:untyped</code>.</p></li><li><p> [<a id="dt-untypedAtomic" title="xs:untypedAtomic">Definition</a>: <code>xs:untypedAtomic</code> is an <a title="atomic type" class="termref" href="#dt-atomic-type">atomic type</a> that is used to denote untyped atomic data, such as text that has not been assigned a more specific type.] An attribute that has been validated in <code>skip</code> mode is represented in the <a title="data model" class="termref" href="#dt-datamodel">data model</a> by an attribute node with the <a title="type annotation" class="termref" href="#dt-type-annotation">type annotation</a><code>xs:untypedAtomic</code>. No predefined schema types are derived from <code>xs:untypedAtomic</code>.</p></li><li><p> [<a id="dt-dayTimeDuration" title="xs:dayTimeDuration">Definition</a>: <code>xs:dayTimeDuration</code> is derived by restriction from <code>xs:duration</code>. The lexical representation of <code>xs:dayTimeDuration</code> is restricted to contain only day, hour, minute, and second components.] </p></li><li><p> [<a id="dt-yearMonthDuration" title="xs:yearMonthDuration">Definition</a>: <code>xs:yearMonthDuration</code> is derived by restriction from <code>xs:duration</code>. The lexical representation of <code>xs:yearMonthDuration</code> is restricted to contain only year and month components.] </p></li><li><p> [<a id="dt-anyAtomicType" title="xs:anyAtomicType">Definition</a>: <code>xs:anyAtomicType</code> is an <a title="atomic type" class="termref" href="#dt-atomic-type">atomic type</a> that includes all atomic items (and no values that are not atomic). Its base type is <code>xs:anySimpleType</code> from which all simple types, including atomic, list, and union types, are derived. All primitive atomic types, such as <code>xs:decimal</code> and <code>xs:string</code>, have <code>xs:anyAtomicType</code> as their base type.] </p><div class="note"><p class="prefix"><b>Note:</b></p><p><code>xs:anyAtomicType</code> will not appear as the type of an actual value in an <a title="XDM instance" class="termref" href="#dt-data-model-instance">XDM instance</a>.</p></div></li><li><p> [<a id="dt-xs-error" title="xs:error">Definition</a>: <code>xs:error</code> is a simple type with no value space. It is defined in <a href="https://www.w3.org/TR/xmlschema11-1/#xsd-error">Section 3.16.7.3 xs:error </a><sup><small>XS11-1</small></sup> and can be used in the <a href="#id-sequencetype-syntax"><b>3.1 Sequence Types</b></a> to raise errors.] </p></li></ol><p>The relationships among the schema types in the <code>xs</code> namespace are illustrated in Figure 2. A more complete description of the XQuery 4.0 type hierarchy can be found in <a href="https://qt4cg.org/specifications/xpath-functions-40/#datatypes">Section 1.8 Type System</a><sup><small>FO</small></sup>.</p><img src="types.jpg" alt="Type Hierarchy Diagram"><p>Figure 2: Hierarchy of Schema Types used in XQuery 4.0.</p></div></div><div class="div1"><h2><a id="id-expressions"></a>4 Expressions</h2><p>This section discusses each of the basic kinds of expression. Each kind of expression has a name such as <code>PathExpr</code>, which is introduced on the left side of the grammar production that defines the expression. Since XQuery 4.0 is a composable language, each kind of expression is defined in terms of other expressions whose operators have a higher precedence. In this way, the precedence of operators is represented explicitly in the grammar.</p><p>The order in which expressions are discussed in this document does not reflect the order of operator precedence. In general, this document introduces the simplest kinds of expressions first, followed by more complex expressions. For the complete grammar, see Appendix [<a href="#nt-bnf"><b>A XQuery 4.0 Grammar</b></a>].</p><p><span class="xquery"> [<a id="dt-query" title="query">Definition</a>: A <b>query</b> consists of one or more <a title="module" class="termref" href="#dt-module">modules</a>.] If a query is executable, one of its modules has a <a title="query body" class="termref" href="#dt-queryBody">Query Body</a> containing an expression whose value is the result of the query. An expression is represented in the XQuery grammar by the symbol <a href="#doc-xquery40-Expr">Expr</a>.</span></p><a id="d3e14452"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-Expr"></a><code><a href="#prod-xquery40-Expr">Expr</a></code></td><td>::=</td><td><code>(<a href="#doc-xquery40-ExprSingle">ExprSingle</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-ExprSingle"></a><code><a href="#prod-xquery40-ExprSingle">ExprSingle</a></code></td><td>::=</td><td><span style="display: none;" class="delete_version"><code><a href="#doc-xquery40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xquery40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xquery40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xquery40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xquery40-IfExpr">IfExpr</a><br>| <a href="#doc-xquery40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xquery40-OrExpr">OrExpr</a></code></span><span style="display: none;" class="add_version"><code><a href="#doc-xquery40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xquery40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xquery40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xquery40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xquery40-IfExpr">IfExpr</a><br>| <a href="#doc-xquery40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xquery40-PipelineExpr">PipelineExpr</a></code></span><span class="modify_version"><code><a href="#doc-xquery40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xquery40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xquery40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xquery40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xquery40-IfExpr">IfExpr</a><br>| <a href="#doc-xquery40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xquery40-OrExpr"><span class="deltaxml-old" style="background:#FF5555">OrExpr</span></a><a href="#doc-xquery40-PipelineExpr"><span class="deltaxml-new" style="background:#90EE90">PipelineExpr</span></a></code></span></td></tr></tbody></table><p>The XQuery 4.0 operator that has lowest precedence is the <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a>, which is used to combine two operands to form a sequence. As shown in the grammar, a general expression (<a href="#doc-xquery40-Expr">Expr</a>) can consist of multiple <a href="#doc-xquery40-ExprSingle">ExprSingle</a> operands, separated by commas.</p><p>The name <a href="#doc-xquery40-ExprSingle">ExprSingle</a> denotes an expression that does not contain a top-level <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a> (despite its name, an <a href="#doc-xquery40-ExprSingle">ExprSingle</a> may evaluate to a sequence containing more than one item.)</p><p>The symbol <a href="#doc-xquery40-ExprSingle">ExprSingle</a> is used in various places in the grammar where an expression is not allowed to contain a top-level comma. For example, each of the arguments of a function call must be a <a href="#doc-xquery40-ExprSingle">ExprSingle</a>, because commas are used to separate the arguments of a function call.</p><p>After the comma, the expressions that have next lowest precedence are <span class="xquery"><a href="#doc-xquery40-FLWORExpr">FLWORExpr</a>,</span><a href="#doc-xquery40-QuantifiedExpr">QuantifiedExpr</a>, <span class="xquery"><a href="#doc-xquery40-SwitchExpr">SwitchExpr</a>, <a href="#doc-xquery40-TypeswitchExpr">TypeswitchExpr</a>, </span><a href="#doc-xquery40-IfExpr">IfExpr</a>, <span class="xquery"><a href="#doc-xquery40-TryCatchExpr">TryCatchExpr</a>, </span> and <a href="#doc-xquery40-OrExpr">OrExpr</a>. Each of these expressions is described in a separate section of this document.</p><div class="div2"><h3><a id="comments"></a>4.1 Comments</h3><a id="d3e14566"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-Comment"></a><code><a href="#prod-xquery40-Comment">Comment</a></code></td><td>::=</td><td><code>"(:" (<a href="#doc-xquery40-CommentContents">CommentContents</a> | <a href="#doc-xquery40-Comment">Comment</a>)* ":)"</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-comments">gn: comments</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-CommentContents"></a><code><a href="#prod-xquery40-CommentContents">CommentContents</a></code></td><td>::=</td><td><code>(<a href="#prod-xquery40-Char">Char</a>+ - (Char* ('(:' | ':)') Char*))</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>Comments may be used to provide information relevant to programmers who read <span class="xquery">a query, either in the <a title="Prolog" class="termref" href="#dt-prolog">Prolog</a> or in the <a title="query body" class="termref" href="#dt-queryBody">Query Body</a></span> . Comments are lexical constructs only, and do not affect <span class="xquery">query</span> processing.</p><p>Comments are strings, delimited by the symbols <code>(:</code> and <code>:)</code>. Comments may be nested.</p><p>A comment may be used anywhere <a title="ignorable whitespace" class="termref" href="#IgnorableWhitespace">ignorable whitespace</a> is allowed (see <a href="#DefaultWhitespaceHandling"><b>A.3.5.1 Default Whitespace Handling</b></a>).</p><p>The following is an example of a comment:</p><div class="exampleInner"><pre xml:space="preserve">(: Houston, we have a problem :)</pre></div></div><div class="div2"><h3><a id="id-primary-expressions"></a>4.2 Primary Expressions</h3><p> [<a id="dt-primary-expression" title="primary expression">Definition</a>: <b>Primary expressions</b> are the basic primitives of the language. They include literals, variable references, context value references, <span class="xquery">constructors, </span> and function calls. A primary expression may also be created by enclosing any expression in parentheses, which is sometimes helpful in controlling the precedence of operators.] <span class="xquery">Node Constructors are described in <a href="#id-constructors"><b>4.12 Node Constructors</b></a>.</span>Map and Array Constructors are described in <a href="#id-maps"><b>4.14.1 Maps</b></a> and <a href="#id-arrays"><b>4.14.2 Arrays</b></a>. <span class="xquery">String Constructors are described in <a href="#id-string-constructors"><b>4.9.3 String Constructors</b></a>.</span></p><a id="d3e14659"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-PrimaryExpr"></a><code><a href="#prod-xquery40-PrimaryExpr">PrimaryExpr</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-Literal">Literal</a><br>| <a href="#doc-xquery40-VarRef">VarRef</a><br>| <a href="#doc-xquery40-ParenthesizedExpr">ParenthesizedExpr</a><br>| <a href="#doc-xquery40-ContextValueRef">ContextValueRef</a><br>| <a href="#doc-xquery40-FunctionCall">FunctionCall</a><br>| <a href="#doc-xquery40-OrderedExpr">OrderedExpr</a><br>| <a href="#doc-xquery40-UnorderedExpr">UnorderedExpr</a><br>| <a href="#doc-xquery40-NodeConstructor">NodeConstructor</a><br>| <a href="#doc-xquery40-FunctionItemExpr">FunctionItemExpr</a><br>| <a href="#doc-xquery40-MapConstructor">MapConstructor</a><br>| <a href="#doc-xquery40-ArrayConstructor">ArrayConstructor</a><br>| <a href="#doc-xquery40-StringTemplate">StringTemplate</a><br>| <a href="#doc-xquery40-StringConstructor">StringConstructor</a><br>| <a href="#doc-xquery40-UnaryLookup">UnaryLookup</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-FunctionItemExpr"></a><code><a href="#prod-xquery40-FunctionItemExpr">FunctionItemExpr</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-NamedFunctionRef">NamedFunctionRef</a> | <a href="#doc-xquery40-InlineFunctionExpr">InlineFunctionExpr</a></code></td></tr></tbody></table><div class="div3"><h4><a id="id-literals"></a>4.2.1 Literals</h4><a id="d3e14751"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-Literal"></a><code><a href="#prod-xquery40-Literal">Literal</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-NumericLiteral">NumericLiteral</a> | <a href="#doc-xquery40-StringLiteral">StringLiteral</a></code></td></tr></tbody></table><p> [<a id="dt-literal" title="literal">Definition</a>: A <b>literal</b> is a direct syntactic representation of an atomic item.] XQuery 4.0 supports two kinds of literals: numeric literals and string literals.</p><div class="div4"><h5><a id="id-numeric-literals"></a>4.2.1.1 Numeric Literals</h5><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-filter-expression">⬇</a>&nbsp;<a href="#id-function-coercion">⬆</a></p><ol><li><p> Numeric literals can now be written in hexadecimal or binary notation; and underscores can be included for readability. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/429">429</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/433">433</a>&nbsp;25 April 2023]</i></p></li></ol></div><a id="d3e14777"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-NumericLiteral"></a><code><a href="#prod-xquery40-NumericLiteral">NumericLiteral</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-IntegerLiteral">IntegerLiteral</a> | <a href="#doc-xquery40-HexIntegerLiteral">HexIntegerLiteral</a> | <a href="#doc-xquery40-BinaryIntegerLiteral">BinaryIntegerLiteral</a> | <a href="#doc-xquery40-DecimalLiteral">DecimalLiteral</a> | <a href="#doc-xquery40-DoubleLiteral">DoubleLiteral</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-IntegerLiteral"></a><code><a href="#prod-xquery40-IntegerLiteral">IntegerLiteral</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-Digits">Digits</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-HexIntegerLiteral"></a><code><a href="#prod-xquery40-HexIntegerLiteral">HexIntegerLiteral</a></code></td><td>::=</td><td><code>"0x" <a href="#doc-xquery40-HexDigits">HexDigits</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-BinaryIntegerLiteral"></a><code><a href="#prod-xquery40-BinaryIntegerLiteral">BinaryIntegerLiteral</a></code></td><td>::=</td><td><code>"0b" <a href="#doc-xquery40-BinaryDigits">BinaryDigits</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-DecimalLiteral"></a><code><a href="#prod-xquery40-DecimalLiteral">DecimalLiteral</a></code></td><td>::=</td><td><code>("." <a href="#doc-xquery40-Digits">Digits</a>) | (<a href="#doc-xquery40-Digits">Digits</a> "." <a href="#doc-xquery40-Digits">Digits</a>?)</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-DoubleLiteral"></a><code><a href="#prod-xquery40-DoubleLiteral">DoubleLiteral</a></code></td><td>::=</td><td><code>(("." <a href="#doc-xquery40-Digits">Digits</a>) | (<a href="#doc-xquery40-Digits">Digits</a> ("." <a href="#doc-xquery40-Digits">Digits</a>?)?)) [eE] [+-]? <a href="#doc-xquery40-Digits">Digits</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-Digits"></a><code><a href="#prod-xquery40-Digits">Digits</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-DecDigit">DecDigit</a> ((<a href="#doc-xquery40-DecDigit">DecDigit</a> | "_")* <a href="#doc-xquery40-DecDigit">DecDigit</a>)?</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-DecDigit"></a><code><a href="#prod-xquery40-DecDigit">DecDigit</a></code></td><td>::=</td><td><code>[0-9]</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-HexDigits"></a><code><a href="#prod-xquery40-HexDigits">HexDigits</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-HexDigit">HexDigit</a> ((<a href="#doc-xquery40-HexDigit">HexDigit</a> | "_")* <a href="#doc-xquery40-HexDigit">HexDigit</a>)?</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-HexDigit"></a><code><a href="#prod-xquery40-HexDigit">HexDigit</a></code></td><td>::=</td><td><code>[0-9a-fA-F]</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-BinaryDigits"></a><code><a href="#prod-xquery40-BinaryDigits">BinaryDigits</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-BinaryDigit">BinaryDigit</a> ((<a href="#doc-xquery40-BinaryDigit">BinaryDigit</a> | "_")* <a href="#doc-xquery40-BinaryDigit">BinaryDigit</a>)?</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-BinaryDigit"></a><code><a href="#prod-xquery40-BinaryDigit">BinaryDigit</a></code></td><td>::=</td><td><code>[01]</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>The value of a numeric literal is determined as follows (taking the rules in order):</p><ol class="enumar"><li><p>Underscore characters are stripped out. Underscores may be included in a numeric literal to aid readability, but have no effect on the value. For example, <code>1_000_000</code> is equivalent to <code>1000000</code>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Underscores must not appear at the beginning or end of a sequence of digits, only in intermediate positions. Multiple adjacent underscores are allowed.</p></div></li><li><p>A <code>HexIntegerLiteral</code> represents a non-negative integer expressed in hexadecimal: for example <code>0xffff</code> represents the integer 65535, and <code>0xFFFF_FFFF</code> represents the integer 4294967295.</p></li><li><p>A <code>BinaryIntegerLiteral</code> represents a non-negative integer expressed in binary: for example <code>0b101</code> represents the integer 5, and <code>0b1111_1111</code> represents the integer 255.</p></li><li><p>The value of a <b>numeric literal</b> containing no <code>.</code> and no <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:integer</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:integer</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li><li><p>The value of a numeric literal containing <code>.</code> but no <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:decimal</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:decimal</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li><li><p>The value of a numeric literal containing an <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:double</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:double</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li></ol><div class="note"><p class="prefix"><b>Note:</b></p><p>The value of a numeric literal is always non-negative. An expression may appear to include a negative number such as <code>-1</code>, but this is technically an arithmetic expression comprising a unary minus operator followed by a numeric literal.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The effect of the above rules is that in the case of an integer or decimal literal, a dynamic error [<a href="https://qt4cg.org/specifications/xpath-functions-40/#ERRFOAR0002" title="err:FOAR0002">err:FOAR0002</a>]<sup><small>FO40</small></sup> will generally be raised if the literal is outside the range of values supported by the implementation (other options are available: see <a href="https://qt4cg.org/specifications/xpath-functions-40/#op.numeric">Section 4.2 Arithmetic operators on numeric values</a><sup><small>FO</small></sup> for details.)</p><p class="xquery">The limits of numeric datatypes are specified in <a href="#id-data-model-conformance"><b>6.3 Data Model Conformance</b></a>.</p></div><p>Here are some examples of numeric literals:</p><ul><li><p><code>12</code> denotes the <code>xs:integer</code> value twelve.</p></li><li><p><code>1_000_000</code> denotes the <code>xs:integer</code> value one million.</p></li><li><p><code>12.5</code> denotes the <code>xs:decimal</code> value twelve and one half.</p></li><li><p><code>3.14159_26535_89793e0</code> is an <code>xs:double</code> value representing the mathematical constant <var>π</var> to 15 decimal places. </p></li><li><p><code>125E2</code> denotes the <code>xs:double</code> value twelve thousand, five hundred.</p></li><li><p><code>0xffff</code> denotes the <code>xs:integer</code> value 65535.</p></li><li><p><code>0b1000_0001</code> denotes the <code>xs:integer</code> value 129.</p></li></ul></div><div class="div4"><h5><a id="id-string-literal"></a>4.2.1.2 String Literals</h5><a id="d3e15148"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-StringLiteral"></a><code><a href="#prod-xquery40-StringLiteral">StringLiteral</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-AposStringLiteral">AposStringLiteral</a> | <a href="#doc-xquery40-QuotStringLiteral">QuotStringLiteral</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-AposStringLiteral"></a><code><a href="#prod-xquery40-AposStringLiteral">AposStringLiteral</a></code></td><td>::=</td><td><code>"'" (<a href="#doc-xquery40-PredefinedEntityRef">PredefinedEntityRef</a> | <a href="#doc-xquery40-CharRef">CharRef</a> | <a href="#doc-xquery40-EscapeApos">EscapeApos</a> | [^'&amp;])* "'"</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-QuotStringLiteral"></a><code><a href="#prod-xquery40-QuotStringLiteral">QuotStringLiteral</a></code></td><td>::=</td><td><code>'"' (<a href="#doc-xquery40-PredefinedEntityRef">PredefinedEntityRef</a> | <a href="#doc-xquery40-CharRef">CharRef</a> | <a href="#doc-xquery40-EscapeQuot">EscapeQuot</a> | [^"&amp;])* '"'</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-PredefinedEntityRef"></a><code><a href="#prod-xquery40-PredefinedEntityRef">PredefinedEntityRef</a></code></td><td>::=</td><td><code>"&amp;" ("lt" | "gt" | "amp" | "quot" | "apos") ";"</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-CharRef"></a><code><a href="#prod-xquery40-CharRef">CharRef</a></code></td><td>::=</td><td><code><a href="https://www.w3.org/TR/REC-xml/#NT-CharRef">[http://www.w3.org/TR/REC-xml#NT-CharRef]</a><sup><small>XML</small></sup></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-xml-version">xgc: xml-version</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-EscapeQuot"></a><code><a href="#prod-xquery40-EscapeQuot">EscapeQuot</a></code></td><td>::=</td><td><code>'""'</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-EscapeApos"></a><code><a href="#prod-xquery40-EscapeApos">EscapeApos</a></code></td><td>::=</td><td><code>"''"</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>The value of a <b>string literal</b> is an atomic item whose type is <code>xs:string</code> and whose value is the string denoted by the characters between the delimiting apostrophes or quotation marks. If the literal is delimited by apostrophes, two adjacent apostrophes within the literal are interpreted as a single apostrophe. Similarly, if the literal is delimited by quotation marks, two adjacent quotation marks within the literal are interpreted as one quotation mark.</p><p class="xquery"> [<a id="dt-predefined-entity-reference" title="predefined entity reference">Definition</a>: A <b>predefined entity reference</b> is a short sequence of characters, beginning with an ampersand, that represents a single character that might otherwise have syntactic significance.] Each predefined entity reference is replaced by the character it represents when the string literal is processed. The predefined entity references recognized by XPath and XQuery are as follows:</p><table style="width:60%; border:1px solid" class="medium"><tbody><tr><th style="text-align:center">Entity Reference</th><th style="text-align:center">Character Represented</th></tr><tr><td style="text-align:center"><code>&amp;lt;</code></td><td style="text-align:center"><code>&lt;</code></td></tr><tr><td style="text-align:center"><code>&amp;gt;</code></td><td style="text-align:center"><code>&gt;</code></td></tr><tr><td style="text-align:center"><code>&amp;amp;</code></td><td style="text-align:center"><code>&amp;</code></td></tr><tr><td style="text-align:center"><code>&amp;quot;</code></td><td style="text-align:center"><code>"</code></td></tr><tr><td style="text-align:center"><code>&amp;apos;</code></td><td style="text-align:center"><code>'</code></td></tr></tbody></table><p class="xquery"> [<a id="dt-character-reference" title="character reference">Definition</a>: A <b>character reference</b> is an XML-style reference to a <a href="#Unicode">[Unicode]</a> character, identified by its decimal or hexadecimal codepoint.] For example, the character <span class="unicode-codepoint">U+20AC</span> (<span class="unicode-name">EURO SIGN</span>, <code>€</code>) can be represented by the character reference <code>&amp;#8364;</code> or <code>&amp;#x20ac;</code>. Character references are normatively defined in Section 4.1 of the XML specification (it is <a title="implementation defined" class="termref" href="#dt-implementation-defined">implementation-defined</a> whether the rules in <a href="#XML">[XML 1.0]</a> or <a href="#XML1.1">[XML 1.1]</a> apply.) A <a title="static error" class="termref" href="#dt-static-error">static error</a> [<a href="#ERRXQST0090" title="err:XQST0090">err:XQST0090</a>] is raised if a character reference does not identify a valid character in the version of XML that is in use.</p><p>Here are some examples of string literals:</p><ul><li><p><code>"He said, ""I don't like it."""</code> denotes a string containing two quotation marks and one apostrophe.</p></li><li class="xquery"><p><code>"Ben &amp;amp; Jerry&amp;apos;s"</code> denotes the <code>xs:string</code> value <code>"Ben &amp; Jerry's"</code>.</p></li><li class="xquery"><p><code>"&amp;#8364;99.50"</code> denotes the <code>xs:string</code> value <code>"€99.50"</code>.</p></li><li><p>In XQuery, the string literal <code>"&amp;lt;"</code> denotes a string of length 1 containing the single character <code>"&lt;"</code>. In XPath, the string literal <code>"&amp;lt;"</code> denotes a string of length 4 containing the four characters <code>"&amp;"</code>, <code>"l"</code>, <code>"t"</code>, <code>";"</code>. (However, when the XPath expression is embedded in an XML document, the sequence <code>"&amp;lt;"</code> will typically have already been converted to <code>"&lt;"</code> by the XML parser.)</p></li></ul><div class="note"><p class="prefix"><b>Note:</b></p><p>When XPath or XQuery expressions are embedded in contexts where quotation marks have special significance, such as inside XML attributes, or in string literals in a host language such as Java or C#, then additional escaping may be needed.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>Fixed string values can also be written as string templates: see <a href="#id-string-templates"><b>4.9.2 String Templates</b></a>. A string template with no enclosed expressions, such as <code>`Jamaica`</code> evaluates to the same value as the string literals <code>"Jamaica"</code> or <code>'Jamaica'</code>. A string template can contain both single and double quotation marks: <code>`He said: "I don't like it"`</code>. However, there there are some subtle differences:</p><ul><li><p>In string literals, the treatment of character and entity references such as <code>&amp;amp;</code> varies between XQuery and XPath; in string templates, such references are not expanded in either language.</p></li><li><p>String templates can only be used where an expression is expected. String literals are also used in some non-expression contexts, for example in defining an enumeration type: see <a href="#id-enumeration-types"><b>3.2.6 Enumeration Types</b></a>.</p></li><li><p>Curly brackets (<span class="unicode-codepoint">U+007B</span> (<span class="unicode-name">LEFT CURLY BRACKET</span>, <code>{</code>) and <span class="unicode-codepoint">U+007D</span> (<span class="unicode-name">RIGHT CURLY BRACKET</span>, <code>}</code>) ) and backticks (<span class="unicode-codepoint">U+0060</span> (<span class="unicode-name">GRAVE ACCENT, BACKTICK</span>, <code>`</code>) ) have a reserved meaning in string templates.</p></li></ul></div></div><div class="div4"><h5><a id="id-constants-other-types"></a>4.2.1.3 Constants of Other Types</h5><p> The <code>xs:boolean</code> values <code>true</code> and <code>false</code> can be constructed by calls to the <a title="system function" class="termref" href="#dt-system-function">system functions</a><code>fn:true()</code> and <code>fn:false()</code>, respectively. </p><p>Values of other simple types can be constructed by calling the <a title="constructor function" class="termref" href="#dt-constructor-function">constructor function</a> for the given type. The constructor functions for XML Schema built-in types are defined in <a href="https://qt4cg.org/specifications/xpath-functions-40/#constructor-functions-for-xsd-types">Section 20.1 Constructor functions for XML Schema built-in atomic types</a><sup><small>FO</small></sup>. In general, the name of a constructor function for a given type is the same as the name of the type (including its namespace). For example:</p><ul><li><p><code>xs:integer("12")</code> returns the integer value twelve.</p></li><li><p><code>xs:date("2001-08-25")</code> returns an item whose type is <code>xs:date</code> and whose value represents the date 25th August 2001.</p></li><li><p><code>xs:dayTimeDuration("PT5H")</code> returns an item whose type is <code>xs:dayTimeDuration</code> and whose value represents a duration of five hours.</p></li></ul><p>Constructor functions can also be used to create special values that have no literal representation, as in the following examples: </p><ul><li><p><code>xs:float("NaN")</code> returns the special floating-point value, "Not a Number."</p></li><li><p><code>xs:double("INF")</code> returns the special double-precision value, "positive infinity."</p></li></ul><p>Constructor functions are available for all simple types, including union types. For example, if <code>my:dt</code> is a user-defined union type whose member types are <code>xs:date</code>, <code>xs:time</code>, and <code>xs:dateTime</code>, then the expression <code>my:dt("2011-01-10")</code> creates an atomic item of type <code>xs:date</code>. The rules follow XML Schema validation rules for union types: the effect is to choose the first member type that accepts the given string in its lexical space.</p><p>It is also possible to construct values of various types by using a <code>cast</code> expression. For example:</p><ul><li><p><code>9 cast as hatsize</code> returns the atomic item <code>9</code> whose type is <code>hatsize</code>.</p></li></ul></div></div><div class="div3"><h4><a id="id-variables"></a>4.2.2 Variable References</h4><a id="d3e15561"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-VarRef"></a><code><a href="#prod-xquery40-VarRef">VarRef</a></code></td><td>::=</td><td><code>"$" <a href="#doc-xquery40-EQName">EQName</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e14479.doc-xquery40-EQName"></a><code>EQName</code></td><td>::=</td><td><code><a href="#doc-xquery40-QName">QName</a> | <a href="#doc-xquery40-URIQualifiedName">URIQualifiedName</a></code></td></tr></tbody></table><p> [<a id="dt-variable-reference" title="variable reference">Definition</a>: A <b>variable reference</b> is an EQName preceded by a $-sign.] An unprefixed variable reference is in no namespace. Two variable references are equivalent if their <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QNames</a> are equal (as defined by the <code>eq</code> operator). The scope of a variable binding is defined separately for each kind of expression that can bind variables.</p><p>Every variable reference must match a name in the <a title="in-scope variables" class="termref" href="#dt-in-scope-variables">in-scope variables</a>. </p><p>Every variable binding has a static scope. The scope defines where references to the variable can validly occur. It is a <a title="static error" class="termref" href="#dt-static-error">static error</a> [<a href="#ERRXPST0008" title="err:XPST0008">err:XPST0008</a>] to reference a variable that is not in scope. If a variable is bound in the <a title="static context" class="termref" href="#dt-static-context">static context</a> for an expression, that variable is in scope for the entire expression except where it is occluded by another binding that uses the same name within that scope.</p><p class="xquery">A reference to a variable that was declared <code>external</code>, but was not bound to a value by the external environment, raises a <a title="dynamic error" class="termref" href="#dt-dynamic-error">dynamic error</a> [<a href="#ERRXPDY0002" title="err:XPDY0002">err:XPDY0002</a>].</p><p> At evaluation time, the value of a variable reference is the value to which the relevant variable is bound.</p></div><div class="div3"><h4><a id="id-context-value-references"></a>4.2.3 Context Value References</h4><a id="d3e15622"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-ContextValueRef"></a><code><a href="#prod-xquery40-ContextValueRef">ContextValueRef</a></code></td><td>::=</td><td><code>"."</code></td></tr></tbody></table><p>A <b>context value reference</b> evaluates to the <a title="context value" class="termref" href="#dt-context-value">context value</a>.</p><p>In many syntactic contexts, the context value will be a single item. For example this applies on the right-hand side of the <code>/</code> or <code>!</code> operators, or within a <a href="#doc-xquery40-Predicate">Predicate</a>.</p><p>If the <a title="context value" class="termref" href="#dt-context-value">context value</a> is <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#dt-absent">absent</a><sup><small>DM</small></sup>, a context value reference raises a <a title="type error" class="termref" href="#dt-type-error">type error</a> [<a href="#ERRXPDY0002" title="err:XPDY0002">err:XPDY0002</a>].</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Being absent is not the same thing as being empty.</p></div></div><div class="div3"><h4><a id="id-paren-expressions"></a>4.2.4 Parenthesized Expressions</h4><a id="d3e15658"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-ParenthesizedExpr"></a><code><a href="#prod-xquery40-ParenthesizedExpr">ParenthesizedExpr</a></code></td><td>::=</td><td><code>"(" <a href="#doc-xquery40-Expr">Expr</a>? ")"</code></td></tr></tbody></table><p>Parentheses may be used to override the precedence rules. For example, the expression <code>(2 + 4) * 5</code> evaluates to thirty, since the parenthesized expression <code>(2 + 4)</code> is evaluated first and its result is multiplied by five. Without parentheses, the expression <code>2 + 4 * 5</code> evaluates to twenty-two, because the multiplication operator has higher precedence than the addition operator.</p><p>Empty parentheses are used to denote an empty sequence, as described in <a href="#construct_seq"><b>4.7.1 Sequence Concatenation</b></a>.</p></div><div class="div3"><h4><a id="id-enclosed-expr"></a>4.2.5 Enclosed Expressions</h4><p><a id="d3e15686"></a></p><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-EnclosedExpr"></a><code><a href="#prod-xquery40-EnclosedExpr">EnclosedExpr</a></code></td><td>::=</td><td><code>"{" <a href="#doc-xquery40-Expr">Expr</a>? "}"</code></td></tr></tbody></table><p> [<a id="dt-enclosed-expression" title="enclosed expression">Definition</a>: An <b>enclosed expression</b> is an instance of the <a href="#doc-xquery40-EnclosedExpr">EnclosedExpr</a> production, which allows an optional expression within curly brackets.] [<a id="dt-content-expression" title="content expression">Definition</a>: In an <a title="enclosed expression" class="termref" href="#dt-enclosed-expression">enclosed expression</a>, the optional expression enclosed in curly brackets is called the <b>content expression</b>.] If the <a title="content expression" class="termref" href="#dt-content-expression">content expression</a> is not provided explicitly, the content expression is <code>()</code>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Despite the name, an enclosed expression is not actually an expression in its own right; rather it is a construct that is used in the grammar of many other expressions.</p></div></div></div><div class="div2"><h3><a id="id-postfix-expression"></a>4.3 Postfix Expressions</h3><a id="d3e15722"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-PostfixExpr"></a><code><a href="#prod-xquery40-PostfixExpr">PostfixExpr</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-PrimaryExpr">PrimaryExpr</a> | <a href="#doc-xquery40-FilterExpr">FilterExpr</a> | <a href="#doc-xquery40-DynamicFunctionCall">DynamicFunctionCall</a> | <a href="#doc-xquery40-LookupExpr">LookupExpr</a> | <a href="#doc-xquery40-FilterExprAM">FilterExprAM</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e14611.doc-xquery40-FilterExpr"></a><code>FilterExpr</code></td><td>::=</td><td><code><a href="#doc-xquery40-PostfixExpr">PostfixExpr</a><a href="#doc-xquery40-Predicate">Predicate</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e14612.doc-xquery40-DynamicFunctionCall"></a><code>DynamicFunctionCall</code></td><td>::=</td><td><code><a href="#doc-xquery40-PostfixExpr">PostfixExpr</a><a href="#doc-xquery40-PositionalArgumentList">PositionalArgumentList</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e14613.doc-xquery40-LookupExpr"></a><code>LookupExpr</code></td><td>::=</td><td><code><a href="#doc-xquery40-PostfixExpr">PostfixExpr</a><a href="#doc-xquery40-Lookup">Lookup</a></code></td></tr></tbody></table><p>A postfix expression takes one of the following forms:</p><ul><li><p> [<a id="dt-filter-expression" title="filter expression">Definition</a>: A <b>filter expression</b> is an expression in the form <code>E1[E2]</code>: its effect is to return those items from the value of <code>E1</code> that satisfy the predicate in E2.] </p><p>Filter expressions are described in <a href="#id-filter-expression"><b>4.4 Filter Expressions</b></a>.</p><p>An example of a filter expression is <code>(1 to 100)[. mod 2 = 0]</code> which returns all even numbers in the range 1 to 100.</p><p>The base expression <code>E1</code> can itself be a postfix expression, so multiple predicates are allowed, in the form <code>E1[E2][E3][E4]</code>.</p></li><li><p>An expression (other than a raw EQName) followed by an argument list in parentheses (that is, <code>E1(E2, E3, ...)</code>) is referred to as a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-invocation">dynamic function call</a>. Its effect is to evaluate <code>E1</code> to obtain a function, and then call that function, with <code>E2</code>, <code>E3</code>, <code>...</code> as arguments. Dynamic function calls are described in <a href="#id-dynamic-function-invocation"><b>4.5.2.1 Dynamic Function Calls</b></a>.</p><p>An example of a dynamic function call is <code>$f("a", 2)</code> where the value of variable <code>$f</code> must be a function item.</p></li><li><p>A <code>lookup-expression</code> takes the form <code>E1?K</code>, where <code>E1</code> is an expression returning a sequence of maps or arrays, and <code>K</code> is a key specifier, which indicates which entries in a map, or members in an array, should be selected.</p><p>Lookup expressions are described in <a href="#id-postfix-lookup"><b>4.14.3.1 Postfix Lookup Expressions</b></a>.</p><p>An example of a lookup expression is <code>$emp?name</code>, where the value of variable <code>$emp</code> is a map, and the string <code>"name"</code> is the key of one of the entries in the map.</p></li></ul><p>Postfix expressions are evaluated from left-to-right. For example, the expression <code>$E1[E2]?(E3)(E4)</code> is evaluated by first evaluating the filter expression <code>$E1[E2]</code> to produce a sequence of maps and arrays (say <code>$S</code>), then evaluating the lookup expression <code>$S?(E3)</code> to produce a function item (say <code>$F</code>), then evaluating the dynamic function call <code>$F(E4)</code> to produce the final result.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>The grammar for postfix expressions is defined here in a way designed to link clearly to the semantics of the different kinds of expression. For parsing purposes, the equivalent production rule:</p><div class="exampleInner"><pre xml:space="preserve">PostfixExpr := PrimaryExpr (Predicate | PositionalArgumentList | Lookup)*</pre></div><p>(as used in XPath 3.1) is probably more convenient.</p></div></div><div class="div2"><h3><a id="id-filter-expression"></a>4.4 Filter Expressions</h3><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-function-calls">⬇</a>&nbsp;<a href="#id-numeric-literals">⬆</a></p><ol><li><p> The value of a predicate in a filter expression can now be a sequence of integers. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/816">816</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/996">996</a>&nbsp;6 February 2024]</i></p></li></ol></div><a id="d3e15901"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-FilterExpr"></a><code><a href="#prod-xquery40-FilterExpr">FilterExpr</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-PostfixExpr">PostfixExpr</a><a href="#doc-xquery40-Predicate">Predicate</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-Predicate"></a><code><a href="#prod-xquery40-Predicate">Predicate</a></code></td><td>::=</td><td><code>"[" <a href="#doc-xquery40-Expr">Expr</a> "]"</code></td></tr></tbody></table><p>A filter expression consists of a base expression followed by a predicate, which is an expression written in square brackets. The result of the filter expression consists of the items returned by the base expression, filtered by applying the predicate to each item in turn. The ordering of the items returned by a filter expression is the same as their order in the result of the primary expression.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Where the expression before the square brackets is a <a href="#doc-xquery40-ReverseStep">ReverseStep</a> or <a href="#doc-xquery40-ForwardStep">ForwardStep</a>, the expression is technically not a filter expression but an <a href="#doc-xquery40-AxisStep">AxisStep</a>. There are minor differences in the semantics: see <a href="#id-predicate"><b>4.6.5 Predicates within Steps</b></a></p></div><p>Here are some examples of filter expressions:</p><ul><li><p>Given a sequence of products in a variable, return only those products whose price is greater than 100.</p><div class="exampleInner"><pre xml:space="preserve">$products[price gt 100]</pre></div></li><li><p>List all the integers from 1 to 100 that are divisible by 5. (See <a href="#construct_seq"><b>4.7.1 Sequence Concatenation</b></a> for an explanation of the <code>to</code> operator.)</p><div class="exampleInner"><pre xml:space="preserve">(1 to 100)[. mod 5 eq 0]</pre></div></li><li><p>The result of the following expression is the integer 25:</p><div class="exampleInner"><pre xml:space="preserve">(21 to 29)[5]</pre></div></li><li><p>The following example returns the fifth through ninth items in the sequence bound to variable <code>$orders</code>.</p><div class="exampleInner"><pre xml:space="preserve">$orders[5 to 9]</pre></div></li><li><p>The following example illustrates the use of a filter expression as a <a title="step" class="termref" href="#dt-step">step</a> in a <a title="path expression" class="termref" href="#dt-path-expression">path expression</a>. It returns the last chapter or appendix within the book bound to variable <code>$book</code>:</p><div class="exampleInner"><pre xml:space="preserve">$book/(chapter | appendix)[last()]</pre></div></li></ul><p>For each item in the input sequence, the predicate expression is evaluated using an <b>inner focus</b>, defined as follows: The context value is the item currently being tested against the predicate. The context size is the number of items in the input sequence. The context position is the position of the context value within the input sequence. </p><p>For each item in the input sequence, the result of the predicate expression is coerced to an <code>xs:boolean</code> value, called the <a title="predicate truth value" class="termref" href="#dt-predicate-truth-value">predicate truth value</a>, as described below. Those items for which the predicate truth value is <code>true</code> are retained, and those for which the predicate truth value is <code>false</code> are discarded.</p><p> [<a id="dt-predicate-truth-value" title="predicate truth value">Definition</a>: The <b>predicate truth value</b> of a value <code>$V</code> is the result of the expression <code>if ($V instance of xs:numeric+) then ($V = position()) else fn:boolean($V)</code>.] </p><p>Expanding this definition, the predicate truth value can be obtained by applying the following rules, in order:</p><ol class="enumar"><li><p>If the value <var>V</var> of the predicate expression is a sequence whose first item is an instance of the type <code>xs:numeric</code>, then:</p><ol class="enumla"><li><p><var>V</var> must be an instance of the type <code>xs:numeric+</code> (that is, every item in <var>V</var> must be numeric). A type error [<a href="https://qt4cg.org/specifications/xpath-functions-40/#ERRFORG0006" title="err:FORG0006">err:FORG0006</a>]<sup><small>FO40</small></sup> is raised if this is not the case.</p></li><li><p>The predicate truth value is <code>true</code> if <var>V</var> is equal (by the <code>=</code> operator) to the <b>context position</b>, and is <code>false</code> otherwise.</p></li></ol><p>In effect this means that an item in the input sequence is selected if its position in the sequence is equal to one or more of the numeric values in the predicate. For example, the predicate <code>[3 to 5]</code> is true for the third, fourth, and fifth items in the input sequence.</p><p> [<a id="dt-numeric-predicate" title="numeric predicate">Definition</a>: A predicate whose predicate expression returns a value of type <code>xs:numeric+</code> is called a <b>numeric predicate</b>.] </p><div class="note"><p class="prefix"><b>Note:</b></p><p>It is possible, though not generally useful, for the value of a numeric predicate to depend on the focus, and thus to differ for different items in the input sequence. For example, the predicate <code>[xs:integer(@seq)]</code> selects those items in the input sequence whose <code>@seq</code> attribute is numerically equal to their position in the input sequence.</p><p>It is also possible, and again not generally useful, for the value of the predicate to be numeric for some items in the input sequence, and boolean for others. For example, the predicate <code>[@special otherwise last()]</code> is true for an item that either has an <code>@special</code> attribute, or is the last item in the input sequence.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The truth value of a numeric predicate does not depend on the order of the numbers in <var>V</var>. The predicates <code>[ 1, 2, 3 ]</code> and <code>[ 3, 2, 1 ]</code> have exactly the same effect. The items in the result of a filter expression always retain the ordering of the input sequence.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The truth value of a numeric predicate whose value is non-integral or non-positive is always false.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>Beware that using boolean operators (<code>and</code>, <code>or</code>, <code>not()</code>) with numeric values may not have the intended effect. For example the predicate <code>[1 or last()]</code> selects every item in the sequence, because <code>or</code> operates on the <a title="effective boolean value" class="termref" href="#dt-ebv">effective boolean value</a> of its operands. The required effect can be achieved with the predicate <code>[1, last()]</code>.</p></div></li><li><p>Otherwise, the predicate truth value is the <a title="effective boolean value" class="termref" href="#dt-ebv">effective boolean value</a> of the predicate expression.</p></li></ol></div><div class="div2"><h3><a id="id-functions"></a>4.5 Functions</h3><p>Functions in XQuery 4.0 arise in two ways:</p><ul><li><p>A <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> contains information about a family of functions with the same name and a defined arity range. These functions are in most cases known statically (they appear in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a>), but there may be further function definitions that are known only dynamically (appearing in the <a title="dynamically known function definitions" class="termref" href="#dt-dynamically-known-function-definitions">dynamically known function definitions</a>).</p></li><li><p><a title="function item" class="termref" href="#dt-function-item">Function items</a> are XDM items that can be called using a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-call">dynamic function call</a>. They are values that can be bound to variables, passed as arguments, returned as function results, and generally manipulated in the same way as other XDM values.</p></li></ul><p>The functions defined by a statically known <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> can be invoked using a <a title="static function call" class="termref" href="#dt-static-function-call">static function call</a>. <a title="function item" class="termref" href="#dt-function-item">Function items</a> corresponding to these definitions can also be obtained, as dynamic values, by evaluating a <a title="named function reference" class="termref" href="#dt-named-function-ref">named function reference</a>. <a title="function item" class="termref" href="#dt-function-item">Function items</a> can also be obtained using the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-function-lookup"><code>fn:function-lookup</code></a> function: in this case the function name and arity do not need to be known statically, and the function definition need not be present in the <a title="static context" class="termref" href="#dt-static-context">static context</a>, so long as it is in the <a title="dynamic context" class="termref" href="#dt-dynamic-context">dynamic context</a>.</p><p>Static and dynamic function calls are described in the following sections.</p><div class="div3"><h4><a id="id-static-functions"></a>4.5.1 Static Function Calls</h4><p>The <a title="static context" class="termref" href="#dt-static-context">static context</a> for an expression includes a set of <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a>. Every <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context has a name (which is an <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a>) and an <a title="arity range" class="termref" href="#dt-arity-range">arity range</a>, which is a range of permitted arities for calls on that function. Two <a title="function definition" class="termref" href="#dt-function-definition">function definitions</a> having the same name must not have overlapping arity ranges. This means that for a given static function call, it is possible to identify the target function definition in the static context unambiguously from knowledge of the function name and the number of supplied arguments.</p><p>A <a title="static function call" class="termref" href="#dt-static-function-call">static function call</a> is bound to a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context by matching the name and arity. If the function call has <var>P</var> positional arguments followed by <var>K</var> keyword arguments, then the required arity is <var>P+K</var>, and the static context must include a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> whose name matches the <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a> in the function call, and whose <a title="arity range" class="termref" href="#dt-arity-range">arity range</a> includes this required arity. This is the function chosen to be called. The result of the function is obtained by evaluating the expression that forms its implementation, with a dynamic context that provides values for all the declared parameters, initialized as described in <a href="#id-eval-static-function-call"><b>4.5.1.2 Evaluating Static Function Calls</b></a> below.</p><p>Similarly, a function reference of the form <code>f#N</code> binds to a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context whose name matches <var>f</var> where <code>MinP ≤ N and MaxP ≥ N</code>. The result of evaluating a function reference is a <a title="function item" class="termref" href="#dt-function-item">function item</a> which can be called using a dynamic function call. Function items are never variadic and their arguments are always supplied positionally. For example, the function reference <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-concat"><code>fn:concat#3</code></a> returns a function item with arity 3, which is always called by supplying three positional arguments, and whose effect is the same as a static call on <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-concat"><code>fn:concat</code></a> with three positional arguments. </p><p>The detailed rules for evaluating static function calls and function references are defined in subsequent sections.</p><div class="div4"><h5><a id="id-function-calls"></a>4.5.1.1 Static Function Call Syntax</h5><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-inline-func">⬇</a>&nbsp;<a href="#id-filter-expression">⬆</a></p><ol><li><p> Keyword arguments are allowed on static function calls, as well as positional arguments. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/155">155</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/159">159</a>&nbsp;30 September 2020]</i></p></li></ol></div><a id="d3e16234"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-FunctionCall"></a><code><a href="#prod-xquery40-FunctionCall">FunctionCall</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-EQName">EQName</a><a href="#doc-xquery40-ArgumentList">ArgumentList</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-reserved-function-names">xgc: reserved-function-names</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-parens">gn: parens</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-ArgumentList"></a><code><a href="#prod-xquery40-ArgumentList">ArgumentList</a></code></td><td>::=</td><td><code>"(" ((<a href="#doc-xquery40-PositionalArguments">PositionalArguments</a> ("," <a href="#prod-xquery40-KeywordArguments">KeywordArguments</a>)?) | <a href="#prod-xquery40-KeywordArguments">KeywordArguments</a>)? ")"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e15060.doc-xquery40-PositionalArguments"></a><code>PositionalArguments</code></td><td>::=</td><td><code>(<a href="#doc-xquery40-Argument">Argument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-Argument"></a><code><a href="#prod-xquery40-Argument">Argument</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-ExprSingle">ExprSingle</a> | <a href="#doc-xquery40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-ArgumentPlaceholder"></a><code><a href="#prod-xquery40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td><td>::=</td><td><code>"?"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e15063.doc-xquery40-KeywordArguments"></a><code>KeywordArguments</code></td><td>::=</td><td><code>(<a href="#doc-xquery40-KeywordArgument">KeywordArgument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-KeywordArgument"></a><code><a href="#prod-xquery40-KeywordArgument">KeywordArgument</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-EQName">EQName</a> ":=" <a href="#doc-xquery40-Argument">Argument</a></code></td></tr></tbody></table><p> [<a id="dt-static-function-call" title="static function call">Definition</a>: A <b>static function call</b> consists of an EQName followed by a parenthesized list of zero or more arguments.] </p><p>The argument list consists of zero or more positional arguments, followed by zero or more keyword arguments.</p><p> [<a id="dt-arg-expr" title="argument expression">Definition</a>: An argument to a function call is either an <b>argument expression</b> or an <a href="#doc-xquery40-ArgumentPlaceholder">ArgumentPlaceholder</a> (<code>?</code>); in both cases it may either be supplied positionally, or identified by a name (called a keyword).] </p><p>This section is concerned with static function calls in which none of the arguments are <a href="#doc-xquery40-ArgumentPlaceholder">ArgumentPlaceholders</a>. Calls using one or more <a href="#doc-xquery40-ArgumentPlaceholder">ArgumentPlaceholders</a> are covered in the section <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p>If the function name supplied in a static function call is an unprefixed <a title="lexical QName" class="termref" href="#dt-qname">lexical QName</a>, it is expanded using the <a title="default function namespace" class="termref" href="#dt-default-function-namespace">default function namespace</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a>. </p><p> The <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a> used as the function name and the number of arguments used in the static function call (the required arity) must match the name and arity range of a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a><span> using the rules defined in the previous section</span>; if there is no match, a <a title="static error" class="termref" href="#dt-static-error">static error</a> is raised [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>]. </p><p>Evaluation of static function calls is described in <a href="#id-eval-static-function-call"><b>4.5.1.2 Evaluating Static Function Calls</b></a> .</p><p>Since the arguments of a function call are separated by commas, any <a title="argument expression" class="termref" href="#dt-arg-expr">argument expression</a> that contains a top-level <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a> must be enclosed in parentheses. Here are some illustrative examples of static function calls:</p><ul><li><p><code>my:three-argument-function(1, 2, 3)</code> denotes a static function call with three <span>positional</span> arguments. <span>The corresponding function declaration must define at least three parameters, and may define more, provided they are optional.</span></p></li><li><p><code>my:two-argument-function((1, 2), 3)</code> denotes a static function call with two arguments, the first of which is a sequence of two values. <span>The corresponding function declaration must define at least two parameters, and may define more, provided they are optional.</span></p></li><li><p><code>my:two-argument-function(1, ())</code> denotes a static function call with two arguments, the second of which is an empty sequence.</p></li><li><p><code>my:one-argument-function((1, 2, 3))</code> denotes a static function call with one argument that is a sequence of three values. </p></li><li><p><code>my:one-argument-function(( ))</code> denotes a static function call with one argument that is an empty sequence.</p></li><li><p><code>my:zero-argument-function( )</code> denotes a static function call with zero arguments.</p></li><li><p><code>lang(node := $n, language := 'de')</code> is a static function call with two keyword arguments. The corresponding function declaration defines two parameters, a required parameter <code>language</code> and an optional parameter <code>node</code>. This call supplies values for both parameters. It is equivalent to the call <code>fn:lang('de', $n)</code>. Note that the keyword arguments are in a different order from the parameter declarations. </p></li><li><p><code>sort(//employee, key := fn($e) { xs:decimal($e/salary) })</code> is a static function call with one positional argument and one keyword argument. The corresponding function declaration defines three parameters, a required parameter <code>$input</code>, an optional parameter <code>$collation</code>, and an optional parameter <code>$key</code> This call supplies values for the first and third parameters, leaving the second parameter (<code>$collation</code>) to take its default value. The default value of the <code>$collation</code> parameter is given as <code>fn:default-collation()</code>, so the value supplied to the function is the default collation from the dynamic context of the caller. It is equivalent to the call <code>fn:sort(//employee, fn:default-collation(), fn($e) { xs:decimal($e/salary) })</code>. </p></li></ul><p>An <code>EQName</code> in a <code>KeywordArgument</code> is expanded to a QName value; if there is no prefix, then the name is in no namespace (otherwise the prefix is resolved in the usual way). The keywords used in a function call (after expansion to QNames) must be distinct [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>]; [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>].</p></div><div class="div4"><h5><a id="id-eval-static-function-call"></a>4.5.1.2 Evaluating Static Function Calls</h5><p>This section applies to static function calls where none of the arguments is an <code>ArgumentPlaceholder</code>. For function calls involving placeholders, see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p> When a static function call <var>FC</var> is evaluated with respect to a static context <var>SC</var> and a dynamic context <var>DC</var>, the result is obtained as follows: </p><ol class="enumar"><li><p> The <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> to be used is found in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a> of <var>SC</var>. </p><p>The <b>required arity</b> is the total number of arguments in the function call, including both positional and keyword arguments.</p><p> There can be at most one <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a> component of <var>SC</var> whose function name matches the expanded QName in <var>FC</var> and whose <a title="arity range" class="termref" href="#dt-arity-range">arity range</a> includes the arity of <var>FC</var>’s <code>ArgumentList</code>. </p><p>If there is no such <a title="function definition" class="termref" href="#dt-function-definition">function definition</a>, a static error [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>] is raised.</p></li><li><p>Each parameter in the <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> is matched to an argument expression as follows:</p><ol class="enumla"><li><p>If there are <var>N</var> positional arguments in the function call <var>FC</var>, then the corresponding argument expressions are matched pairwise to the first <var>N</var> parameters in the declaration. For this purpose the required parameters and optional parameters in <var>FD</var> are concatenated into a single list, in order.</p></li><li><p>Any keyword arguments in <var>FC</var> are then matched to parameters (whether required or optional) in <var>FD</var> by comparing the keyword used in <var>FC</var> with the paramater name declared in <var>FD</var>. Each keyword must match the name of a declared parameter [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>], and this must be one that has not already been matched to a positional argument. [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>].</p></li><li><p>If any required parameter has not been matched to any argument in <var>FC</var> by applying the above rules, a static error is reported [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>] </p></li><li><p>If any optional parameter has not been matched to any argument in <var>FC</var> by applying the above rules, then the parameter is matched to the default value expression for that parameter in <var>FD</var>.</p></li></ol></li><li><p> Each argument expression established by the above rules is evaluated with respect to DC. The order of argument evaluation is <a title="implementation   dependent" class="termref" href="#dt-implementation-dependent">implementation dependent</a> and it is not required that an argument be evaluated if the function body can be evaluated without evaluating that argument.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>All argument expressions, including default value expressions, are evaluated in the dynamic context of the function call. It is therefore possible to use a default value expression such as <code>.</code>, or <code>/</code>, or <code>fn:current-dateTime()</code>, whose value depends on the dynamic context of the function call.</p></div><p>If the expression used for the default value of a parameter has no dependencies on the dynamic context, then an implementation <span class="verb">may</span> choose to reuse the same value on repeated function calls rather than re-evaluating it on each function call.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>This is relevant, for example, if the expression constructs new nodes.</p></div></li><li><p>The result of evaluating the argument expression is converted to the required type (the declared type associated with the corresponding parameter in the function declaration, defaulting to <code>item()*</code>) by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>.</p><p><span>This applies both to explicitly supplied arguments, and to values obtained by evaluating default value expressions. In both cases a type error will be raised if the value (after coercion) does not match the required type.</span></p></li><li><p>The result of the function call is obtained as follows:</p><ul><li><p><var>FD</var>’s <span>body</span> is invoked in an implementation-dependent way. The processor makes the following information available to that invocation: </p><ul><li><p>The converted argument values;</p></li><li><p>If the function is <a title="context dependent" class="termref" href="#dt-context-dependent">context dependent</a>, the static context <var>SC</var> and dynamic context <var>DC</var> of the function call. </p></li></ul></li><li><p>The result is converted to the required type (the declared return type in the function declaration, defaulting to <code>item()*</code>) by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>.</p><p>The result of applying the coercion rules is either an instance of <var>FD</var>’s return type or a dynamic error. This result is then the result of evaluating <var>FC</var>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>A host language may define alternative rules for processing the result, especially in the case of external functions implemented using a non-XDM type system.</p></div></li><li><p> Errors raised by system functions are defined in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>. </p></li><li class="xquery"><p> Errors raised by external functions are <a title="implementation defined" class="termref" href="#dt-implementation-defined">implementation-defined</a> (see <a href="#id-consistency-constraints"><b>2.3.6 Consistency Constraints</b></a>). </p></li></ul><div class="example"><div class="exampleHeader"><a id="d3e16696"></a>Example: A System Function</div><p>The following function call uses the function <a href="https://qt4cg.org/specifications/xpath-functions-40/#func-base-uri">Section 2.1.5 fn:base-uri</a><sup><small>FO</small></sup>. Use of <code>SC</code> and <code>DC</code> and errors raised by this function are all defined in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>.</p><div class="exampleInner"><pre xml:space="preserve">base-uri()</pre></div></div></li></ol></div></div><div class="div3"><h4><a id="id-dynamic-functions"></a>4.5.2 Function Items</h4><p>A <a title="function item" class="termref" href="#dt-function-item">function item</a> is an XDM value that can be bound to a variable, or manipulated in various ways by XQuery 4.0 expressions. The most significant such expression is a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-call">dynamic function call</a>, which supplies values of arguments and evaluates the function to produce a result.</p><p>The syntax of dynamic function calls is defined in <a href="#id-dynamic-function-invocation"><b>4.5.2.1 Dynamic Function Calls</b></a>.</p><p>A number of constructs can be used to produce a <a title="function item" class="termref" href="#dt-function-item">function item</a>, notably:</p><ul><li><p>A <b>named function reference</b> (see <a href="#id-named-function-ref"><b>4.5.2.4 Named Function References</b></a>) constructs a function item by reference to <a title="function definition" class="termref" href="#dt-function-definition">function definitions</a> in the static context. For example, <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-node-name"><code>fn:node-name#1</code></a> returns a function item whose effect is to call the static <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-node-name"><code>fn:node-name</code></a> function with one argument.</p></li><li><p>An <b>inline function</b> (see <a href="#id-inline-func"><b>4.5.2.5 Inline Function Expressions</b></a> ) constructs a function item whose <span>body</span> is defined locally. For example, the construct <code>fn($x) { $x + 1 }</code> returns a function item whose effect is to increment the value of the supplied argument.</p></li><li><p>A <b>partial function application</b> (see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>) derives one function item from another by supplying the values of some of its arguments. For example, <code>fn:ends-with(?, ".txt")</code> returns a function item with one argument that tests whether the supplied string ends with the substring <code>".txt"</code>.</p></li><li><p>Maps and arrays are also function items. See <a href="#id-map-constructors"><b>4.14.1.1 Map Constructors</b></a> and <a href="#id-array-constructors"><b>4.14.2.1 Array Constructors</b></a>.</p></li><li><p>The <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-function-lookup"><code>fn:function-lookup</code></a> function can be called to discover functions that are present in the <a title="dynamic context" class="termref" href="#dt-dynamic-context">dynamic context</a>.</p></li><li><p>The <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-load-xquery-module"><code>fn:load-xquery-module</code></a> function can be called to load functions dynamically from an external XQuery library module.</p></li><li><p>Some system functions such as <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-random-number-generator"><code>fn:random-number-generator</code></a> and <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-op"><code>fn:op</code></a> return a <a title="function item" class="termref" href="#dt-function-item">function item</a> as their result.</p></li></ul><p>These constructs are described in detail in the following sections, or in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>.</p><div class="div4"><h5><a id="id-dynamic-function-invocation"></a>4.5.2.1 Dynamic Function Calls</h5><a id="d3e16805"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-DynamicFunctionCall"></a><code><a href="#prod-xquery40-DynamicFunctionCall">DynamicFunctionCall</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-PostfixExpr">PostfixExpr</a><a href="#doc-xquery40-PositionalArgumentList">PositionalArgumentList</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-PositionalArgumentList"></a><code><a href="#prod-xquery40-PositionalArgumentList">PositionalArgumentList</a></code></td><td>::=</td><td><code>"(" <a href="#doc-xquery40-PositionalArguments">PositionalArguments</a>? ")"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-PositionalArguments"></a><code><a href="#prod-xquery40-PositionalArguments">PositionalArguments</a></code></td><td>::=</td><td><code>(<a href="#doc-xquery40-Argument">Argument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e15569.doc-xquery40-Argument"></a><code>Argument</code></td><td>::=</td><td><code><a href="#doc-xquery40-ExprSingle">ExprSingle</a> | <a href="#doc-xquery40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e15570.doc-xquery40-ArgumentPlaceholder"></a><code>ArgumentPlaceholder</code></td><td>::=</td><td><code>"?"</code></td></tr></tbody></table><p> [<a id="dt-dynamic-function-invocation" title="dynamic function call">Definition</a>: A <b>dynamic function call</b> consists of a base expression that returns the function and a parenthesized list of zero or more arguments (<a title="argument expression" class="termref" href="#dt-arg-expr">argument expressions</a> or ArgumentPlaceholders).] </p><p> A dynamic function call is evaluated as described in <a href="#id-eval-dynamic-function-call"><b>4.5.2.2 Evaluating Dynamic Function Calls</b></a>. </p><p>The following are examples of some dynamic function calls:</p><ul><li><p>This example calls the function contained in <code>$f</code>, passing the arguments 2 and 3: </p><div class="exampleInner"><pre xml:space="preserve">$f(2, 3)</pre></div></li><li><p>This example fetches the second item from sequence <code>$f</code>, treats it as a function and calls it, passing an <code>xs:string</code> argument: </p><div class="exampleInner"><pre xml:space="preserve">$f[2]("Hi there")</pre></div></li><li><p>This example calls the function <code>$f</code> passing no arguments, and filters the result with a positional predicate: </p><div class="exampleInner"><pre xml:space="preserve">$f()[2]</pre></div></li></ul><div class="note"><p class="prefix"><b>Note:</b></p><p>Arguments in a dynamic function call are always supplied positionally.</p></div></div><div class="div4"><h5><a id="id-eval-dynamic-function-call"></a>4.5.2.2 Evaluating Dynamic Function Calls</h5><p>This section applies to dynamic function calls whose arguments do not include an <code>ArgumentPlaceholder</code>. For function calls that include a placeholder, see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p> [<a id="dt-dynamic-function-call" title="dynamic function call">Definition</a>: A <b>dynamic function call</b> is an expression that is evaluated by calling a <a title="function item" class="termref" href="#dt-function-item">function item</a>, which is typically obtained dynamically.] </p><p> When a dynamic function call <var>FC</var> is evaluated, the result is obtained as follows: </p><ol class="enumar"><li><p> The <a title="function item" class="termref" href="#dt-function-item">function item</a><var>FI</var> to be called is obtained by evaluating the base expression of the function call. If this yields a sequence consisting of a single function item whose arity matches the number of arguments in the <code>ArgumentList</code>, let <var>FI</var> denote that function item. Otherwise, a type error is raised [<a href="#ERRXPTY0004" title="err:XPTY0004">err:XPTY0004</a>]. </p><div class="note"><p class="prefix"><b>Note:</b></p><p>Keyword arguments are not allowed in a dynamic function call.</p></div></li><li><p><a title="argument expression" class="termref" href="#dt-arg-expr">Argument expressions</a> are evaluated, producing <b>argument values</b>. The order of argument evaluation is <a title="implementation   dependent" class="termref" href="#dt-implementation-dependent">implementation-dependent</a> and an argument need not be evaluated if the function body can be evaluated without evaluating that argument.</p></li><li><p> Each argument value is converted to the corresponding parameter type in <var>FI</var>’s signature by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>, resulting in a <b>converted argument value</b></p></li><li><p>If <var>FI</var> is a map, it is evaluated as described in <a href="#id-map-lookup"><b>4.14.1.2 Maps as Functions</b></a>.</p></li><li><p>If <var>FI</var> is an array, it is evaluated as described in <a href="#id-array-lookup"><b>4.14.2.2 Arrays as Functions</b></a>.</p></li><li><p> If <var>FI</var>’s <span>body</span> is an XQuery 4.0 expression (for example, if <var>FI</var> is <span class="xquery">a <a title="user-defined function" class="termref" href="#dt-udf">user-defined function</a> or</span> an <a title="anonymous function" class="termref" href="#dt-anonymous-function">anonymous function</a>, or a <a title="partially applied function" class="termref" href="#dt-partially-applied-function">partial application</a> of such a function): </p><ol class="enumla"><li><p><var>FI</var>’s <span>body</span> is evaluated. The static context for this evaluation is the static context of the XQuery 4.0 expression. The dynamic context for this evaluation is obtained by taking the dynamic context of the <span class="xquery">module</span> that contains the <code>FunctionBody</code>, and making the following changes: </p><ul><li><p> The <a title="focus" class="termref" href="#dt-focus">focus</a> (context value, context position, and context size) is <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#dt-absent">absent</a><sup><small>DM</small></sup>. </p></li><li><p> In the <a title="variable values" class="termref" href="#dt-variable-values">variable values</a> component of the dynamic context, each converted argument value is bound to the corresponding parameter name. </p><p><span>When this is done, the converted argument values retain their <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic types</a>, even where these are <a title="subtype" class="termref" href="#dt-subtype">subtypes</a> of the declared parameter types.</span> For example, a function with a parameter <code>$p</code> of type <code>xs:decimal</code> can be called with an argument of type <code>xs:integer</code>, which is derived from <code>xs:decimal</code>. During the processing of this function call, the value of <code>$p</code> inside the body of the function retains its <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic type</a> of <code>xs:integer</code>. </p></li><li><p><var>FI</var>’s nonlocal variable bindings are also added to the <a title="variable values" class="termref" href="#dt-variable-values">variable values</a>. (Note that the names of the nonlocal variables are by definition disjoint from the parameter names, so there can be no conflict.) </p></li></ul></li><li><p> The value returned by evaluating the function body is then converted to the declared return type of <var>FI</var> by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>. The result is then the result of evaluating <var>FC</var>. </p><p> As with argument values, the value returned by a function retains its <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic type</a>, which may be a <a title="subtype" class="termref" href="#dt-subtype">subtype</a> of the declared return type of <var>FI</var>. For example, a function that has a declared return type of <code>xs:decimal</code> may in fact return a value of dynamic type <code>xs:integer</code>. </p></li></ol><div class="example"><div class="exampleHeader"><a id="d3e17083"></a>Example: Derived Types and Nonlocal Variable Bindings</div><p><code>$incr</code> is a nonlocal variable that is available within the function because its variable binding has been added to the variable values of the function.. Even though the parameter and return type of this function are both <code>xs:decimal</code>, the more specific type <code>xs:integer</code> is preserved in both cases.</p><div class="exampleInner"><pre xml:space="preserve">let $incr := 1
+return $f(12.3)</pre></div><p class="xquery">With XQuery 4.0, as a consequence of function coercion, this fails with a type error because the argument supplied in the function call is not of type <code>xs:integer</code>.</p></div></div><div class="div3"><h4><a id="id-coercion-examples"></a>3.4.4 Examples of Coercions</h4><p>This section illustrates the effect of the coercion rules with examples.</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-string"></a>Example: Coercion to <code>xs:string</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:string</code>. For example, the second argument of <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-matches"><code>fn:matches</code></a>, which expects a regular expression. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>"[0-9]"</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>default-language()</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of <code>xs:language</code>, which is a subtype of the required type <code>xs:string</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;[0-9]&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. Unless it has been schema-validated, the typed value will be an instance of <code>xs:untypedAtomic</code>, which is accepted when the required type is <code>xs:string</code>.</p><p>Supplying an element whose type annotation is (say) <code>xs:date</code> will fail with a type error.</p></td></tr><tr><td style="vertical-align:top"><code>xs:anyURI("urn:dummy")</code></td><td style="vertical-align:top"><p>Supplying an instance of <code>xs:anyURI</code> where the expected type is <code>xs:string</code> is permitted; this is one of the pairs of types where implicit casting is allowed.</p></td></tr><tr><td style="vertical-align:top"><code>["a|b"]</code></td><td style="vertical-align:top"><p>Supplying an array holding a single string succeeds, because the rules cause the array to be atomized, and the value after atomization is a single string.</p><p>Supplying an array holding multiple strings would fail.</p></td></tr></tbody></table></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-decimal"></a>Example: Coercion to <code>xs:decimal?</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:decimal?</code>. For example, the first argument of <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-seconds"><code>fn:seconds</code></a>, which expects a decimal number of seconds. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>12.4</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>()</code></td><td style="vertical-align:top"><p>None; an empty sequence is an instance of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>42</code></td><td style="vertical-align:top"><p>None; the supplied value is an instance of <code>xs:integer</code>, which is a subtype of the required type.</p></td></tr><tr><td style="vertical-align:top"><code>math:pi()</code></td><td style="vertical-align:top"><p>The supplied value is an instance of <code>xs:double</code>, which can be converted to <code>xs:decimal</code> under the coercion rules.</p></td></tr><tr><td style="vertical-align:top"><code>("a", "b")[.="c"]</code></td><td style="vertical-align:top"><p>The supplied value is an empty sequence, which is a valid instance of the required type <code>xs:decimal?</code>. However, the processor may (optionally) reject this as an implausible coercion, on the grounds that it can only succeed in one special case, namely where the filter expression selects no values. </p></td></tr><tr><td style="vertical-align:top"><code>(1.5, 2.5, 3.5)</code></td><td style="vertical-align:top"><p>A type error is raised.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;3.14159&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The element node is atomized; unless it has been schema-validated, the result will be <code>"3.14159"</code> as an instance of <code>xs:untypedAtomic</code>. This is converted to an instance of <code>xs:decimal</code> following the rules of the <code>cast as</code> operator.</p></td></tr><tr><td style="vertical-align:top"><code>[1.5]</code></td><td style="vertical-align:top"><p>The array is atomized, and the result is a valid instance of the required type <code>xs:decimal?</code></p></td></tr><tr><td style="vertical-align:top"><code>[]</code></td><td style="vertical-align:top"><p>The array is atomized, and the result is an empty sequence, which is a valid instance of the required type <code>xs:decimal?</code></p></td></tr></tbody></table></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-positive-integer"></a>Example: Coercion to <code>xs:positive-integer</code></div><p>Consider the case where the required type (of a variable, or a function argument) is <code>xs:positive-integer</code>. The table below illustrates the values that might be supplied, and the coercions that are applied.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>12</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:integer</code>. Because the supplied value and the required type, <code>xs:positiveInteger</code>, both come under the primitive type <code>xs:decimal</code>, and the value <code>12</code> is within the value space of <code>xs:positiveInteger</code>, the value is relabeled as an <code>xs:positiveInteger</code> and the call succeeds.</p></td></tr><tr><td style="vertical-align:top"><code>12.1</code></td><td style="vertical-align:top"><p>This fails with a type error, because the <code>xs:decimal</code> value <code>12.1</code> is not a value in the value space of <code>xs:positiveInteger</code>. This is so even though casting to <code>xs:positiveInteger</code> would succeed.</p></td></tr><tr><td style="vertical-align:top"><code>math:pi()</code></td><td style="vertical-align:top"><p>This fails with a type error. A value of type <code>xs:double</code> is accepted where the required type is <code>xs:decimal</code> or <code>xs:float</code>, but not where it is <code>xs:positiveInteger</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;1200&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. If the element has not been schema-validated, the result will be an <code>xs:untypedAtomic</code> item, which is successfully cast to the required type <code>xs:positiveInteger</code>. If the element has been validated against a schema, then coercion succeeds if the typed value would itself be acceptable, for example if it is an <code>xs:positiveInteger</code>, or some other <code>xs:decimal</code> within the value space of <code>xs:positiveInteger</code>.</p></td></tr></tbody></table></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-union"></a>Example: Coercion to a union type</div><p>Consider the first parameter of the function <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a>, whose declared type is <code>(xs:string | xs:positiveInteger)</code>. The rules are the same as if it were a union typed declared in an imported schema.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>"amp"</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:string</code>, which is one of the allowed types. The call therefore succeeds.</p></td></tr><tr><td style="vertical-align:top"><code>"#"</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:string</code>, which is one of the allowed types. As far as the coercion rules are concerned, the call therefore succeeds. Under the semantic rules for the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a> function, however, this value is not accepted; a dynamic error (as distinct from a type error) is therefore raised.</p></td></tr><tr><td style="vertical-align:top"><code>0x25</code></td><td style="vertical-align:top"><p>The supplied value is of type <code>xs:integer</code>. Although this is not one of the allowed types, it is acceptable because coercion of the value to type <code>xs:positiveInteger</code> succeeds. The value is relabeled as an instance of <code>xs:positiveInteger</code>.</p></td></tr><tr><td style="vertical-align:top"><code>&lt;a&gt;0x25&lt;/a&gt;</code></td><td style="vertical-align:top"><p>The supplied element node is atomized. Assuming that the node has not been schema-validated, the result is an instance of <code>xs:untypedAtomic</code>. The member types of the choice are tested in order. Conversion to <code>xs:string</code> with the value "0x25" succeeds, so the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-char"><code>fn:char</code></a> function is called supplying this string; but the function rejects this string as semantically invalid. The same would happen if the value were, say, &lt;a&gt;37&lt;/a&gt;. Supplying such a value requires an explicit cast, for example <code>fn:char( xs:positiveInteger( ./a ))</code>.</p></td></tr></tbody></table></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="eg-coercion-to-choice"></a>Example: Coercion to a choice type</div><p>Suppose the required type is <code>(record(x as xs:decimal, y as xs:decimal, *) | record(size as enum("S", "M", "L", "XL"), *))</code>.</p><table class="medium"><thead><tr><th style="text-align:left">Supplied Value</th><th style="text-align:left">Coercion</th></tr></thead><tbody><tr><td style="vertical-align:top"><code>{ "x": 1, "y": 2, "z": 3 }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of the first record type: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "size": "M" }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of the second record type: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1, "y": 2, "size": "XL" }</code></td><td style="vertical-align:top"><p>The supplied value is an instance of both record types: no coercion is necessary.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1e0, "y": 2e0, "size": "XL" }</code></td><td style="vertical-align:top"><p>The supplied value is not an instance of the first record type because the fields are of type <code>xs:double</code> rather than <code>xs:decimal</code>. It is however an instance of the second record type. It is therefore accepted <em>as is</em>; the fields <code>x</code> and <code>y</code> are not converted from <code>xs:double</code> to <code>xs:decimal</code>.</p></td></tr><tr><td style="vertical-align:top"><code>{ "x": 1e0, "y": 2e0, "size": "XXL" }</code></td><td style="vertical-align:top"><p>The supplied value is not an instance of the first record type because the fields are of type <code>xs:double</code> rather than <code>xs:decimal</code>, and it is not an instance of the second record type because the <code>size</code> value does not match the enumeration type. Coercion is therefore attempted to the first record type, and succeeds. The <code>x</code> and <code>y</code> fields are coerced to <code>xs:decimal</code>, and the <code>size</code> field is accepted <em>as is</em>.</p></td></tr></tbody></table></div></div></div><div class="div2"><h3><a id="id-predefined-types"></a>3.5 Schema Types</h3><p> [<a id="dt-schema-type" title="schema type">Definition</a>: A <b>schema type</b> is a complex type or simple type as defined in the <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> specifications, including built-in types as well as user-defined types.] </p><p>Every schema type is either a <b>complex type</b> or a <b>simple type</b>; simple types are further subdivided into <b>list types</b>, <b>union types</b>, and <b>atomic types</b> (see <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> for definitions and explanations of these terms.)</p><p>A schema type can appear as a type annotation on an element or attribute node. The type annotation on an element node can be a complex type or a simple type; the type annotation on an attribute node is always a simple type. Non-instantiable types such as <code>xs:NOTATION</code> or <code>xs:anyAtomicType</code> never appear as type annotations, but their derived types can be so used. Union types never appear as type annotations; when an element or attribute is validated against a union type, the resulting type annotation will be one of the types in the transitive membership of the union type.</p><p> [<a id="dt-atomic-type" title="atomic type">Definition</a>: An <b>atomic type</b> is a simple <a title="schema type" class="termref" href="#dt-schema-type">schema type</a> whose <a href="https://www.w3.org/TR/xmlschema11-1/#std-variety">{variety}<sup><small>XS11-1</small></sup></a> is <code>atomic</code>.] </p><p>An <b>atomic type</b> is either a built-in atomic type (defined either in the XSD specification or in this specification), or it is a user-defined atomic type included in an imported schema.</p><p>The schema types defined in <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#types-predefined">Section 2.8.3 Predefined Types</a><sup><small>DM</small></sup> are summarized below.</p><p class="xquery">The <a title="in-scope schema type" class="termref" href="#dt-is-types">in-scope schema types</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a> are initialized with certain predefined schema types, including the built-in schema types in the namespace <code>http://www.w3.org/2001/XMLSchema</code>, which has the predefined namespace prefix <code>xs</code>. The schema types in this namespace are defined in <a href="#XMLSchema10">[XML Schema 1.0]</a> or <a href="#XMLSchema11">[XML Schema 1.1]</a> and augmented by additional types defined in <a href="#xpath-datamodel-40">[XQuery and XPath Data Model (XDM) 4.0]</a>. Element and attribute declarations in the <code>xs</code> namespace are not implicitly included in the static context. The schema types defined in <a href="#xpath-datamodel-40">[XQuery and XPath Data Model (XDM) 4.0]</a> are summarized below.</p><ol class="enumar"><li><p> [<a id="dt-untyped" title="xs:untyped">Definition</a>: <code>xs:untyped</code> is used as the <a title="type annotation" class="termref" href="#dt-type-annotation">type annotation</a> of an element node that has not been validated, or has been validated in <code>skip</code> mode.] No predefined schema types are derived from <code>xs:untyped</code>.</p></li><li><p> [<a id="dt-untypedAtomic" title="xs:untypedAtomic">Definition</a>: <code>xs:untypedAtomic</code> is an <a title="atomic type" class="termref" href="#dt-atomic-type">atomic type</a> that is used to denote untyped atomic data, such as text that has not been assigned a more specific type.] An attribute that has been validated in <code>skip</code> mode is represented in the <a title="data model" class="termref" href="#dt-datamodel">data model</a> by an attribute node with the <a title="type annotation" class="termref" href="#dt-type-annotation">type annotation</a><code>xs:untypedAtomic</code>. No predefined schema types are derived from <code>xs:untypedAtomic</code>.</p></li><li><p> [<a id="dt-dayTimeDuration" title="xs:dayTimeDuration">Definition</a>: <code>xs:dayTimeDuration</code> is derived by restriction from <code>xs:duration</code>. The lexical representation of <code>xs:dayTimeDuration</code> is restricted to contain only day, hour, minute, and second components.] </p></li><li><p> [<a id="dt-yearMonthDuration" title="xs:yearMonthDuration">Definition</a>: <code>xs:yearMonthDuration</code> is derived by restriction from <code>xs:duration</code>. The lexical representation of <code>xs:yearMonthDuration</code> is restricted to contain only year and month components.] </p></li><li><p> [<a id="dt-anyAtomicType" title="xs:anyAtomicType">Definition</a>: <code>xs:anyAtomicType</code> is an <a title="atomic type" class="termref" href="#dt-atomic-type">atomic type</a> that includes all atomic items (and no values that are not atomic). Its base type is <code>xs:anySimpleType</code> from which all simple types, including atomic, list, and union types, are derived. All primitive atomic types, such as <code>xs:decimal</code> and <code>xs:string</code>, have <code>xs:anyAtomicType</code> as their base type.] </p><div class="note"><p class="prefix"><b>Note:</b></p><p><code>xs:anyAtomicType</code> will not appear as the type of an actual value in an <a title="XDM instance" class="termref" href="#dt-data-model-instance">XDM instance</a>.</p></div></li><li><p> [<a id="dt-xs-error" title="xs:error">Definition</a>: <code>xs:error</code> is a simple type with no value space. It is defined in <a href="https://www.w3.org/TR/xmlschema11-1/#xsd-error">Section 3.16.7.3 xs:error </a><sup><small>XS11-1</small></sup> and can be used in the <a href="#id-sequencetype-syntax"><b>3.1 Sequence Types</b></a> to raise errors.] </p></li></ol><p>The relationships among the schema types in the <code>xs</code> namespace are illustrated in Figure 2. A more complete description of the XQuery 4.0 type hierarchy can be found in <a href="https://qt4cg.org/specifications/xpath-functions-40/#datatypes">Section 1.8 Type System</a><sup><small>FO</small></sup>.</p><img src="types.jpg" alt="Type Hierarchy Diagram"><p>Figure 2: Hierarchy of Schema Types used in XQuery 4.0.</p></div></div><div class="div1"><h2><a id="id-expressions"></a>4 Expressions</h2><p>This section discusses each of the basic kinds of expression. Each kind of expression has a name such as <code>PathExpr</code>, which is introduced on the left side of the grammar production that defines the expression. Since XQuery 4.0 is a composable language, each kind of expression is defined in terms of other expressions whose operators have a higher precedence. In this way, the precedence of operators is represented explicitly in the grammar.</p><p>The order in which expressions are discussed in this document does not reflect the order of operator precedence. In general, this document introduces the simplest kinds of expressions first, followed by more complex expressions. For the complete grammar, see Appendix [<a href="#nt-bnf"><b>A XQuery 4.0 Grammar</b></a>].</p><p><span class="xquery"> [<a id="dt-query" title="query">Definition</a>: A <b>query</b> consists of one or more <a title="module" class="termref" href="#dt-module">modules</a>.] If a query is executable, one of its modules has a <a title="query body" class="termref" href="#dt-queryBody">Query Body</a> containing an expression whose value is the result of the query. An expression is represented in the XQuery grammar by the symbol <a href="#doc-xquery40-Expr">Expr</a>.</span></p><a id="d3e14452"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-Expr"></a><code><a href="#prod-xquery40-Expr">Expr</a></code></td><td>::=</td><td><code>(<a href="#doc-xquery40-ExprSingle">ExprSingle</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-ExprSingle"></a><code><a href="#prod-xquery40-ExprSingle">ExprSingle</a></code></td><td>::=</td><td><span style="display: none;" class="delete_version"><code><a href="#doc-xquery40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xquery40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xquery40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xquery40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xquery40-IfExpr">IfExpr</a><br>| <a href="#doc-xquery40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xquery40-OrExpr">OrExpr</a></code></span><span style="display: none;" class="add_version"><code><a href="#doc-xquery40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xquery40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xquery40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xquery40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xquery40-IfExpr">IfExpr</a><br>| <a href="#doc-xquery40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xquery40-PipelineExpr">PipelineExpr</a></code></span><span class="modify_version"><code><a href="#doc-xquery40-FLWORExpr">FLWORExpr</a><br>| <a href="#doc-xquery40-QuantifiedExpr">QuantifiedExpr</a><br>| <a href="#doc-xquery40-SwitchExpr">SwitchExpr</a><br>| <a href="#doc-xquery40-TypeswitchExpr">TypeswitchExpr</a><br>| <a href="#doc-xquery40-IfExpr">IfExpr</a><br>| <a href="#doc-xquery40-TryCatchExpr">TryCatchExpr</a><br>| <a href="#doc-xquery40-OrExpr"><span class="deltaxml-old" style="background:#FF5555">OrExpr</span></a><a href="#doc-xquery40-PipelineExpr"><span class="deltaxml-new" style="background:#90EE90">PipelineExpr</span></a></code></span></td></tr></tbody></table><p>The XQuery 4.0 operator that has lowest precedence is the <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a>, which is used to combine two operands to form a sequence. As shown in the grammar, a general expression (<a href="#doc-xquery40-Expr">Expr</a>) can consist of multiple <a href="#doc-xquery40-ExprSingle">ExprSingle</a> operands, separated by commas.</p><p>The name <a href="#doc-xquery40-ExprSingle">ExprSingle</a> denotes an expression that does not contain a top-level <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a> (despite its name, an <a href="#doc-xquery40-ExprSingle">ExprSingle</a> may evaluate to a sequence containing more than one item.)</p><p>The symbol <a href="#doc-xquery40-ExprSingle">ExprSingle</a> is used in various places in the grammar where an expression is not allowed to contain a top-level comma. For example, each of the arguments of a function call must be a <a href="#doc-xquery40-ExprSingle">ExprSingle</a>, because commas are used to separate the arguments of a function call.</p><p><span style="display: none;" class="delete_version">After the comma, the expressions that have next lowest precedence are <span class="xquery"><a href="#doc-xquery40-FLWORExpr">FLWORExpr</a>,</span><a href="#doc-xquery40-QuantifiedExpr">QuantifiedExpr</a>, <span class="xquery"><a href="#doc-xquery40-SwitchExpr">SwitchExpr</a>, <a href="#doc-xquery40-TypeswitchExpr">TypeswitchExpr</a>, </span><a href="#doc-xquery40-IfExpr">IfExpr</a>, <span class="xquery"><a href="#doc-xquery40-TryCatchExpr">TryCatchExpr</a>, </span> and <a href="#doc-xquery40-OrExpr">OrExpr</a>. Each of these expressions is described in a separate section of this document.</span><span style="display: none;" class="add_version">After the comma, the expressions that have next lowest precedence are <span class="xquery"><a href="#doc-xquery40-FLWORExpr">FLWORExpr</a>,</span><a href="#doc-xquery40-QuantifiedExpr">QuantifiedExpr</a>, <span class="xquery"><a href="#doc-xquery40-SwitchExpr">SwitchExpr</a>, <a href="#doc-xquery40-TypeswitchExpr">TypeswitchExpr</a>, </span><a href="#doc-xquery40-IfExpr">IfExpr</a>, <span class="xquery"><a href="#doc-xquery40-TryCatchExpr">TryCatchExpr</a>, </span> and <a href="#doc-xquery40-PipelineExpr">PipelineExpr</a>. Each of these expressions is described in a separate section of this document.</span><span class="modify_version">After the comma, the expressions that have next lowest precedence are <span class="xquery"><a href="#doc-xquery40-FLWORExpr">FLWORExpr</a>,</span><a href="#doc-xquery40-QuantifiedExpr">QuantifiedExpr</a>, <span class="xquery"><a href="#doc-xquery40-SwitchExpr">SwitchExpr</a>, <a href="#doc-xquery40-TypeswitchExpr">TypeswitchExpr</a>, </span><a href="#doc-xquery40-IfExpr">IfExpr</a>, <span class="xquery"><a href="#doc-xquery40-TryCatchExpr">TryCatchExpr</a>, </span> and <a href="#doc-xquery40-OrExpr"><span class="deltaxml-old" style="background:#FF5555">OrExpr</span></a><a href="#doc-xquery40-PipelineExpr"><span class="deltaxml-new" style="background:#90EE90">PipelineExpr</span></a>. Each of these expressions is described in a separate section of this document.</span></p><div class="div2"><h3><a id="comments"></a>4.1 Comments</h3><a id="d3e14566"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-Comment"></a><code><a href="#prod-xquery40-Comment">Comment</a></code></td><td>::=</td><td><code>"(:" (<a href="#doc-xquery40-CommentContents">CommentContents</a> | <a href="#doc-xquery40-Comment">Comment</a>)* ":)"</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-comments">gn: comments</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-CommentContents"></a><code><a href="#prod-xquery40-CommentContents">CommentContents</a></code></td><td>::=</td><td><code>(<a href="#prod-xquery40-Char">Char</a>+ - (Char* ('(:' | ':)') Char*))</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>Comments may be used to provide information relevant to programmers who read <span class="xquery">a query, either in the <a title="Prolog" class="termref" href="#dt-prolog">Prolog</a> or in the <a title="query body" class="termref" href="#dt-queryBody">Query Body</a></span> . Comments are lexical constructs only, and do not affect <span class="xquery">query</span> processing.</p><p>Comments are strings, delimited by the symbols <code>(:</code> and <code>:)</code>. Comments may be nested.</p><p>A comment may be used anywhere <a title="ignorable whitespace" class="termref" href="#IgnorableWhitespace">ignorable whitespace</a> is allowed (see <a href="#DefaultWhitespaceHandling"><b>A.3.5.1 Default Whitespace Handling</b></a>).</p><p>The following is an example of a comment:</p><div class="exampleInner"><pre xml:space="preserve">(: Houston, we have a problem :)</pre></div></div><div class="div2"><h3><a id="id-primary-expressions"></a>4.2 Primary Expressions</h3><p> [<a id="dt-primary-expression" title="primary expression">Definition</a>: <b>Primary expressions</b> are the basic primitives of the language. They include literals, variable references, context value references, <span class="xquery">constructors, </span> and function calls. A primary expression may also be created by enclosing any expression in parentheses, which is sometimes helpful in controlling the precedence of operators.] <span class="xquery">Node Constructors are described in <a href="#id-constructors"><b>4.12 Node Constructors</b></a>.</span>Map and Array Constructors are described in <a href="#id-maps"><b>4.14.1 Maps</b></a> and <a href="#id-arrays"><b>4.14.2 Arrays</b></a>. <span class="xquery">String Constructors are described in <a href="#id-string-constructors"><b>4.9.3 String Constructors</b></a>.</span></p><a id="d3e14659"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-PrimaryExpr"></a><code><a href="#prod-xquery40-PrimaryExpr">PrimaryExpr</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-Literal">Literal</a><br>| <a href="#doc-xquery40-VarRef">VarRef</a><br>| <a href="#doc-xquery40-ParenthesizedExpr">ParenthesizedExpr</a><br>| <a href="#doc-xquery40-ContextValueRef">ContextValueRef</a><br>| <a href="#doc-xquery40-FunctionCall">FunctionCall</a><br>| <a href="#doc-xquery40-OrderedExpr">OrderedExpr</a><br>| <a href="#doc-xquery40-UnorderedExpr">UnorderedExpr</a><br>| <a href="#doc-xquery40-NodeConstructor">NodeConstructor</a><br>| <a href="#doc-xquery40-FunctionItemExpr">FunctionItemExpr</a><br>| <a href="#doc-xquery40-MapConstructor">MapConstructor</a><br>| <a href="#doc-xquery40-ArrayConstructor">ArrayConstructor</a><br>| <a href="#doc-xquery40-StringTemplate">StringTemplate</a><br>| <a href="#doc-xquery40-StringConstructor">StringConstructor</a><br>| <a href="#doc-xquery40-UnaryLookup">UnaryLookup</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-FunctionItemExpr"></a><code><a href="#prod-xquery40-FunctionItemExpr">FunctionItemExpr</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-NamedFunctionRef">NamedFunctionRef</a> | <a href="#doc-xquery40-InlineFunctionExpr">InlineFunctionExpr</a></code></td></tr></tbody></table><div class="div3"><h4><a id="id-literals"></a>4.2.1 Literals</h4><a id="d3e14751"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-Literal"></a><code><a href="#prod-xquery40-Literal">Literal</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-NumericLiteral">NumericLiteral</a> | <a href="#doc-xquery40-StringLiteral">StringLiteral</a></code></td></tr></tbody></table><p> [<a id="dt-literal" title="literal">Definition</a>: A <b>literal</b> is a direct syntactic representation of an atomic item.] XQuery 4.0 supports two kinds of literals: numeric literals and string literals.</p><div class="div4"><h5><a id="id-numeric-literals"></a>4.2.1.1 Numeric Literals</h5><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-filter-expression">⬇</a>&nbsp;<a href="#id-function-coercion">⬆</a></p><ol><li><p> Numeric literals can now be written in hexadecimal or binary notation; and underscores can be included for readability. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/429">429</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/433">433</a>&nbsp;25 April 2023]</i></p></li></ol></div><a id="d3e14777"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-NumericLiteral"></a><code><a href="#prod-xquery40-NumericLiteral">NumericLiteral</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-IntegerLiteral">IntegerLiteral</a> | <a href="#doc-xquery40-HexIntegerLiteral">HexIntegerLiteral</a> | <a href="#doc-xquery40-BinaryIntegerLiteral">BinaryIntegerLiteral</a> | <a href="#doc-xquery40-DecimalLiteral">DecimalLiteral</a> | <a href="#doc-xquery40-DoubleLiteral">DoubleLiteral</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-IntegerLiteral"></a><code><a href="#prod-xquery40-IntegerLiteral">IntegerLiteral</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-Digits">Digits</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-HexIntegerLiteral"></a><code><a href="#prod-xquery40-HexIntegerLiteral">HexIntegerLiteral</a></code></td><td>::=</td><td><code>"0x" <a href="#doc-xquery40-HexDigits">HexDigits</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-BinaryIntegerLiteral"></a><code><a href="#prod-xquery40-BinaryIntegerLiteral">BinaryIntegerLiteral</a></code></td><td>::=</td><td><code>"0b" <a href="#doc-xquery40-BinaryDigits">BinaryDigits</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-DecimalLiteral"></a><code><a href="#prod-xquery40-DecimalLiteral">DecimalLiteral</a></code></td><td>::=</td><td><code>("." <a href="#doc-xquery40-Digits">Digits</a>) | (<a href="#doc-xquery40-Digits">Digits</a> "." <a href="#doc-xquery40-Digits">Digits</a>?)</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-DoubleLiteral"></a><code><a href="#prod-xquery40-DoubleLiteral">DoubleLiteral</a></code></td><td>::=</td><td><code>(("." <a href="#doc-xquery40-Digits">Digits</a>) | (<a href="#doc-xquery40-Digits">Digits</a> ("." <a href="#doc-xquery40-Digits">Digits</a>?)?)) [eE] [+-]? <a href="#doc-xquery40-Digits">Digits</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-Digits"></a><code><a href="#prod-xquery40-Digits">Digits</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-DecDigit">DecDigit</a> ((<a href="#doc-xquery40-DecDigit">DecDigit</a> | "_")* <a href="#doc-xquery40-DecDigit">DecDigit</a>)?</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-DecDigit"></a><code><a href="#prod-xquery40-DecDigit">DecDigit</a></code></td><td>::=</td><td><code>[0-9]</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-HexDigits"></a><code><a href="#prod-xquery40-HexDigits">HexDigits</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-HexDigit">HexDigit</a> ((<a href="#doc-xquery40-HexDigit">HexDigit</a> | "_")* <a href="#doc-xquery40-HexDigit">HexDigit</a>)?</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-HexDigit"></a><code><a href="#prod-xquery40-HexDigit">HexDigit</a></code></td><td>::=</td><td><code>[0-9a-fA-F]</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-BinaryDigits"></a><code><a href="#prod-xquery40-BinaryDigits">BinaryDigits</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-BinaryDigit">BinaryDigit</a> ((<a href="#doc-xquery40-BinaryDigit">BinaryDigit</a> | "_")* <a href="#doc-xquery40-BinaryDigit">BinaryDigit</a>)?</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-BinaryDigit"></a><code><a href="#prod-xquery40-BinaryDigit">BinaryDigit</a></code></td><td>::=</td><td><code>[01]</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>The value of a numeric literal is determined as follows (taking the rules in order):</p><ol class="enumar"><li><p>Underscore characters are stripped out. Underscores may be included in a numeric literal to aid readability, but have no effect on the value. For example, <code>1_000_000</code> is equivalent to <code>1000000</code>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Underscores must not appear at the beginning or end of a sequence of digits, only in intermediate positions. Multiple adjacent underscores are allowed.</p></div></li><li><p>A <code>HexIntegerLiteral</code> represents a non-negative integer expressed in hexadecimal: for example <code>0xffff</code> represents the integer 65535, and <code>0xFFFF_FFFF</code> represents the integer 4294967295.</p></li><li><p>A <code>BinaryIntegerLiteral</code> represents a non-negative integer expressed in binary: for example <code>0b101</code> represents the integer 5, and <code>0b1111_1111</code> represents the integer 255.</p></li><li><p>The value of a <b>numeric literal</b> containing no <code>.</code> and no <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:integer</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:integer</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li><li><p>The value of a numeric literal containing <code>.</code> but no <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:decimal</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:decimal</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li><li><p>The value of a numeric literal containing an <code>e</code> or <code>E</code> character is an atomic item of type <code>xs:double</code>; the value is obtained by casting from <code>xs:string</code> to <code>xs:double</code> as specified in <a href="https://qt4cg.org/specifications/xpath-functions-40/#casting-from-strings">Section 21.2 Casting from xs:string and xs:untypedAtomic</a><sup><small>FO</small></sup>.</p></li></ol><div class="note"><p class="prefix"><b>Note:</b></p><p>The value of a numeric literal is always non-negative. An expression may appear to include a negative number such as <code>-1</code>, but this is technically an arithmetic expression comprising a unary minus operator followed by a numeric literal.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The effect of the above rules is that in the case of an integer or decimal literal, a dynamic error [<a href="https://qt4cg.org/specifications/xpath-functions-40/#ERRFOAR0002" title="err:FOAR0002">err:FOAR0002</a>]<sup><small>FO40</small></sup> will generally be raised if the literal is outside the range of values supported by the implementation (other options are available: see <a href="https://qt4cg.org/specifications/xpath-functions-40/#op.numeric">Section 4.2 Arithmetic operators on numeric values</a><sup><small>FO</small></sup> for details.)</p><p class="xquery">The limits of numeric datatypes are specified in <a href="#id-data-model-conformance"><b>6.3 Data Model Conformance</b></a>.</p></div><p>Here are some examples of numeric literals:</p><ul><li><p><code>12</code> denotes the <code>xs:integer</code> value twelve.</p></li><li><p><code>1_000_000</code> denotes the <code>xs:integer</code> value one million.</p></li><li><p><code>12.5</code> denotes the <code>xs:decimal</code> value twelve and one half.</p></li><li><p><code>3.14159_26535_89793e0</code> is an <code>xs:double</code> value representing the mathematical constant <var>π</var> to 15 decimal places. </p></li><li><p><code>125E2</code> denotes the <code>xs:double</code> value twelve thousand, five hundred.</p></li><li><p><code>0xffff</code> denotes the <code>xs:integer</code> value 65535.</p></li><li><p><code>0b1000_0001</code> denotes the <code>xs:integer</code> value 129.</p></li></ul></div><div class="div4"><h5><a id="id-string-literal"></a>4.2.1.2 String Literals</h5><a id="d3e15148"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-StringLiteral"></a><code><a href="#prod-xquery40-StringLiteral">StringLiteral</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-AposStringLiteral">AposStringLiteral</a> | <a href="#doc-xquery40-QuotStringLiteral">QuotStringLiteral</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-AposStringLiteral"></a><code><a href="#prod-xquery40-AposStringLiteral">AposStringLiteral</a></code></td><td>::=</td><td><code>"'" (<a href="#doc-xquery40-PredefinedEntityRef">PredefinedEntityRef</a> | <a href="#doc-xquery40-CharRef">CharRef</a> | <a href="#doc-xquery40-EscapeApos">EscapeApos</a> | [^'&amp;])* "'"</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-QuotStringLiteral"></a><code><a href="#prod-xquery40-QuotStringLiteral">QuotStringLiteral</a></code></td><td>::=</td><td><code>'"' (<a href="#doc-xquery40-PredefinedEntityRef">PredefinedEntityRef</a> | <a href="#doc-xquery40-CharRef">CharRef</a> | <a href="#doc-xquery40-EscapeQuot">EscapeQuot</a> | [^"&amp;])* '"'</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-PredefinedEntityRef"></a><code><a href="#prod-xquery40-PredefinedEntityRef">PredefinedEntityRef</a></code></td><td>::=</td><td><code>"&amp;" ("lt" | "gt" | "amp" | "quot" | "apos") ";"</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-CharRef"></a><code><a href="#prod-xquery40-CharRef">CharRef</a></code></td><td>::=</td><td><code><a href="https://www.w3.org/TR/REC-xml/#NT-CharRef">[http://www.w3.org/TR/REC-xml#NT-CharRef]</a><sup><small>XML</small></sup></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-xml-version">xgc: xml-version</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-EscapeQuot"></a><code><a href="#prod-xquery40-EscapeQuot">EscapeQuot</a></code></td><td>::=</td><td><code>'""'</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-EscapeApos"></a><code><a href="#prod-xquery40-EscapeApos">EscapeApos</a></code></td><td>::=</td><td><code>"''"</code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#ws-explicit">ws: explicit</a> */</td></tr></tbody></table><p>The value of a <b>string literal</b> is an atomic item whose type is <code>xs:string</code> and whose value is the string denoted by the characters between the delimiting apostrophes or quotation marks. If the literal is delimited by apostrophes, two adjacent apostrophes within the literal are interpreted as a single apostrophe. Similarly, if the literal is delimited by quotation marks, two adjacent quotation marks within the literal are interpreted as one quotation mark.</p><p class="xquery"> [<a id="dt-predefined-entity-reference" title="predefined entity reference">Definition</a>: A <b>predefined entity reference</b> is a short sequence of characters, beginning with an ampersand, that represents a single character that might otherwise have syntactic significance.] Each predefined entity reference is replaced by the character it represents when the string literal is processed. The predefined entity references recognized by XPath and XQuery are as follows:</p><table style="width:60%; border:1px solid" class="medium"><tbody><tr><th style="text-align:center">Entity Reference</th><th style="text-align:center">Character Represented</th></tr><tr><td style="text-align:center"><code>&amp;lt;</code></td><td style="text-align:center"><code>&lt;</code></td></tr><tr><td style="text-align:center"><code>&amp;gt;</code></td><td style="text-align:center"><code>&gt;</code></td></tr><tr><td style="text-align:center"><code>&amp;amp;</code></td><td style="text-align:center"><code>&amp;</code></td></tr><tr><td style="text-align:center"><code>&amp;quot;</code></td><td style="text-align:center"><code>"</code></td></tr><tr><td style="text-align:center"><code>&amp;apos;</code></td><td style="text-align:center"><code>'</code></td></tr></tbody></table><p class="xquery"> [<a id="dt-character-reference" title="character reference">Definition</a>: A <b>character reference</b> is an XML-style reference to a <a href="#Unicode">[Unicode]</a> character, identified by its decimal or hexadecimal codepoint.] For example, the character <span class="unicode-codepoint">U+20AC</span> (<span class="unicode-name">EURO SIGN</span>, <code>€</code>) can be represented by the character reference <code>&amp;#8364;</code> or <code>&amp;#x20ac;</code>. Character references are normatively defined in Section 4.1 of the XML specification (it is <a title="implementation defined" class="termref" href="#dt-implementation-defined">implementation-defined</a> whether the rules in <a href="#XML">[XML 1.0]</a> or <a href="#XML1.1">[XML 1.1]</a> apply.) A <a title="static error" class="termref" href="#dt-static-error">static error</a> [<a href="#ERRXQST0090" title="err:XQST0090">err:XQST0090</a>] is raised if a character reference does not identify a valid character in the version of XML that is in use.</p><p>Here are some examples of string literals:</p><ul><li><p><code>"He said, ""I don't like it."""</code> denotes a string containing two quotation marks and one apostrophe.</p></li><li class="xquery"><p><code>"Ben &amp;amp; Jerry&amp;apos;s"</code> denotes the <code>xs:string</code> value <code>"Ben &amp; Jerry's"</code>.</p></li><li class="xquery"><p><code>"&amp;#8364;99.50"</code> denotes the <code>xs:string</code> value <code>"€99.50"</code>.</p></li><li><p>In XQuery, the string literal <code>"&amp;lt;"</code> denotes a string of length 1 containing the single character <code>"&lt;"</code>. In XPath, the string literal <code>"&amp;lt;"</code> denotes a string of length 4 containing the four characters <code>"&amp;"</code>, <code>"l"</code>, <code>"t"</code>, <code>";"</code>. (However, when the XPath expression is embedded in an XML document, the sequence <code>"&amp;lt;"</code> will typically have already been converted to <code>"&lt;"</code> by the XML parser.)</p></li></ul><div class="note"><p class="prefix"><b>Note:</b></p><p>When XPath or XQuery expressions are embedded in contexts where quotation marks have special significance, such as inside XML attributes, or in string literals in a host language such as Java or C#, then additional escaping may be needed.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>Fixed string values can also be written as string templates: see <a href="#id-string-templates"><b>4.9.2 String Templates</b></a>. A string template with no enclosed expressions, such as <code>`Jamaica`</code> evaluates to the same value as the string literals <code>"Jamaica"</code> or <code>'Jamaica'</code>. A string template can contain both single and double quotation marks: <code>`He said: "I don't like it"`</code>. However, there there are some subtle differences:</p><ul><li><p>In string literals, the treatment of character and entity references such as <code>&amp;amp;</code> varies between XQuery and XPath; in string templates, such references are not expanded in either language.</p></li><li><p>String templates can only be used where an expression is expected. String literals are also used in some non-expression contexts, for example in defining an enumeration type: see <a href="#id-enumeration-types"><b>3.2.6 Enumeration Types</b></a>.</p></li><li><p>Curly brackets (<span class="unicode-codepoint">U+007B</span> (<span class="unicode-name">LEFT CURLY BRACKET</span>, <code>{</code>) and <span class="unicode-codepoint">U+007D</span> (<span class="unicode-name">RIGHT CURLY BRACKET</span>, <code>}</code>) ) and backticks (<span class="unicode-codepoint">U+0060</span> (<span class="unicode-name">GRAVE ACCENT, BACKTICK</span>, <code>`</code>) ) have a reserved meaning in string templates.</p></li></ul></div></div><div class="div4"><h5><a id="id-constants-other-types"></a>4.2.1.3 Constants of Other Types</h5><p> The <code>xs:boolean</code> values <code>true</code> and <code>false</code> can be constructed by calls to the <a title="system function" class="termref" href="#dt-system-function">system functions</a><code>fn:true()</code> and <code>fn:false()</code>, respectively. </p><p>Values of other simple types can be constructed by calling the <a title="constructor function" class="termref" href="#dt-constructor-function">constructor function</a> for the given type. The constructor functions for XML Schema built-in types are defined in <a href="https://qt4cg.org/specifications/xpath-functions-40/#constructor-functions-for-xsd-types">Section 20.1 Constructor functions for XML Schema built-in atomic types</a><sup><small>FO</small></sup>. In general, the name of a constructor function for a given type is the same as the name of the type (including its namespace). For example:</p><ul><li><p><code>xs:integer("12")</code> returns the integer value twelve.</p></li><li><p><code>xs:date("2001-08-25")</code> returns an item whose type is <code>xs:date</code> and whose value represents the date 25th August 2001.</p></li><li><p><code>xs:dayTimeDuration("PT5H")</code> returns an item whose type is <code>xs:dayTimeDuration</code> and whose value represents a duration of five hours.</p></li></ul><p>Constructor functions can also be used to create special values that have no literal representation, as in the following examples: </p><ul><li><p><code>xs:float("NaN")</code> returns the special floating-point value, "Not a Number."</p></li><li><p><code>xs:double("INF")</code> returns the special double-precision value, "positive infinity."</p></li></ul><p>Constructor functions are available for all simple types, including union types. For example, if <code>my:dt</code> is a user-defined union type whose member types are <code>xs:date</code>, <code>xs:time</code>, and <code>xs:dateTime</code>, then the expression <code>my:dt("2011-01-10")</code> creates an atomic item of type <code>xs:date</code>. The rules follow XML Schema validation rules for union types: the effect is to choose the first member type that accepts the given string in its lexical space.</p><p>It is also possible to construct values of various types by using a <code>cast</code> expression. For example:</p><ul><li><p><code>9 cast as hatsize</code> returns the atomic item <code>9</code> whose type is <code>hatsize</code>.</p></li></ul></div></div><div class="div3"><h4><a id="id-variables"></a>4.2.2 Variable References</h4><a id="d3e15561"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-VarRef"></a><code><a href="#prod-xquery40-VarRef">VarRef</a></code></td><td>::=</td><td><code>"$" <a href="#doc-xquery40-EQName">EQName</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e14479.doc-xquery40-EQName"></a><code>EQName</code></td><td>::=</td><td><code><a href="#doc-xquery40-QName">QName</a> | <a href="#doc-xquery40-URIQualifiedName">URIQualifiedName</a></code></td></tr></tbody></table><p> [<a id="dt-variable-reference" title="variable reference">Definition</a>: A <b>variable reference</b> is an EQName preceded by a $-sign.] An unprefixed variable reference is in no namespace. Two variable references are equivalent if their <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QNames</a> are equal (as defined by the <code>eq</code> operator). The scope of a variable binding is defined separately for each kind of expression that can bind variables.</p><p>Every variable reference must match a name in the <a title="in-scope variables" class="termref" href="#dt-in-scope-variables">in-scope variables</a>. </p><p>Every variable binding has a static scope. The scope defines where references to the variable can validly occur. It is a <a title="static error" class="termref" href="#dt-static-error">static error</a> [<a href="#ERRXPST0008" title="err:XPST0008">err:XPST0008</a>] to reference a variable that is not in scope. If a variable is bound in the <a title="static context" class="termref" href="#dt-static-context">static context</a> for an expression, that variable is in scope for the entire expression except where it is occluded by another binding that uses the same name within that scope.</p><p class="xquery">A reference to a variable that was declared <code>external</code>, but was not bound to a value by the external environment, raises a <a title="dynamic error" class="termref" href="#dt-dynamic-error">dynamic error</a> [<a href="#ERRXPDY0002" title="err:XPDY0002">err:XPDY0002</a>].</p><p> At evaluation time, the value of a variable reference is the value to which the relevant variable is bound.</p></div><div class="div3"><h4><a id="id-context-value-references"></a>4.2.3 Context Value References</h4><a id="d3e15622"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-ContextValueRef"></a><code><a href="#prod-xquery40-ContextValueRef">ContextValueRef</a></code></td><td>::=</td><td><code>"."</code></td></tr></tbody></table><p>A <b>context value reference</b> evaluates to the <a title="context value" class="termref" href="#dt-context-value">context value</a>.</p><p>In many syntactic contexts, the context value will be a single item. For example this applies on the right-hand side of the <code>/</code> or <code>!</code> operators, or within a <a href="#doc-xquery40-Predicate">Predicate</a>.</p><p>If the <a title="context value" class="termref" href="#dt-context-value">context value</a> is <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#dt-absent">absent</a><sup><small>DM</small></sup>, a context value reference raises a <a title="type error" class="termref" href="#dt-type-error">type error</a> [<a href="#ERRXPDY0002" title="err:XPDY0002">err:XPDY0002</a>].</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Being absent is not the same thing as being empty.</p></div></div><div class="div3"><h4><a id="id-paren-expressions"></a>4.2.4 Parenthesized Expressions</h4><a id="d3e15658"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-ParenthesizedExpr"></a><code><a href="#prod-xquery40-ParenthesizedExpr">ParenthesizedExpr</a></code></td><td>::=</td><td><code>"(" <a href="#doc-xquery40-Expr">Expr</a>? ")"</code></td></tr></tbody></table><p>Parentheses may be used to override the precedence rules. For example, the expression <code>(2 + 4) * 5</code> evaluates to thirty, since the parenthesized expression <code>(2 + 4)</code> is evaluated first and its result is multiplied by five. Without parentheses, the expression <code>2 + 4 * 5</code> evaluates to twenty-two, because the multiplication operator has higher precedence than the addition operator.</p><p>Empty parentheses are used to denote an empty sequence, as described in <a href="#construct_seq"><b>4.7.1 Sequence Concatenation</b></a>.</p></div><div class="div3"><h4><a id="id-enclosed-expr"></a>4.2.5 Enclosed Expressions</h4><p><a id="d3e15686"></a></p><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-EnclosedExpr"></a><code><a href="#prod-xquery40-EnclosedExpr">EnclosedExpr</a></code></td><td>::=</td><td><code>"{" <a href="#doc-xquery40-Expr">Expr</a>? "}"</code></td></tr></tbody></table><p> [<a id="dt-enclosed-expression" title="enclosed expression">Definition</a>: An <b>enclosed expression</b> is an instance of the <a href="#doc-xquery40-EnclosedExpr">EnclosedExpr</a> production, which allows an optional expression within curly brackets.] [<a id="dt-content-expression" title="content expression">Definition</a>: In an <a title="enclosed expression" class="termref" href="#dt-enclosed-expression">enclosed expression</a>, the optional expression enclosed in curly brackets is called the <b>content expression</b>.] If the <a title="content expression" class="termref" href="#dt-content-expression">content expression</a> is not provided explicitly, the content expression is <code>()</code>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Despite the name, an enclosed expression is not actually an expression in its own right; rather it is a construct that is used in the grammar of many other expressions.</p></div></div></div><div class="div2"><h3><a id="id-postfix-expression"></a>4.3 Postfix Expressions</h3><a id="d3e15722"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-PostfixExpr"></a><code><a href="#prod-xquery40-PostfixExpr">PostfixExpr</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-PrimaryExpr">PrimaryExpr</a> | <a href="#doc-xquery40-FilterExpr">FilterExpr</a> | <a href="#doc-xquery40-DynamicFunctionCall">DynamicFunctionCall</a> | <a href="#doc-xquery40-LookupExpr">LookupExpr</a> | <a href="#doc-xquery40-FilterExprAM">FilterExprAM</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e14611.doc-xquery40-FilterExpr"></a><code>FilterExpr</code></td><td>::=</td><td><code><a href="#doc-xquery40-PostfixExpr">PostfixExpr</a><a href="#doc-xquery40-Predicate">Predicate</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e14612.doc-xquery40-DynamicFunctionCall"></a><code>DynamicFunctionCall</code></td><td>::=</td><td><code><a href="#doc-xquery40-PostfixExpr">PostfixExpr</a><a href="#doc-xquery40-PositionalArgumentList">PositionalArgumentList</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e14613.doc-xquery40-LookupExpr"></a><code>LookupExpr</code></td><td>::=</td><td><code><a href="#doc-xquery40-PostfixExpr">PostfixExpr</a><a href="#doc-xquery40-Lookup">Lookup</a></code></td></tr></tbody></table><p>A postfix expression takes one of the following forms:</p><ul><li><p> [<a id="dt-filter-expression" title="filter expression">Definition</a>: A <b>filter expression</b> is an expression in the form <code>E1[E2]</code>: its effect is to return those items from the value of <code>E1</code> that satisfy the predicate in E2.] </p><p>Filter expressions are described in <a href="#id-filter-expression"><b>4.4 Filter Expressions</b></a>.</p><p>An example of a filter expression is <code>(1 to 100)[. mod 2 = 0]</code> which returns all even numbers in the range 1 to 100.</p><p>The base expression <code>E1</code> can itself be a postfix expression, so multiple predicates are allowed, in the form <code>E1[E2][E3][E4]</code>.</p></li><li><p>An expression (other than a raw EQName) followed by an argument list in parentheses (that is, <code>E1(E2, E3, ...)</code>) is referred to as a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-invocation">dynamic function call</a>. Its effect is to evaluate <code>E1</code> to obtain a function, and then call that function, with <code>E2</code>, <code>E3</code>, <code>...</code> as arguments. Dynamic function calls are described in <a href="#id-dynamic-function-invocation"><b>4.5.2.1 Dynamic Function Calls</b></a>.</p><p>An example of a dynamic function call is <code>$f("a", 2)</code> where the value of variable <code>$f</code> must be a function item.</p></li><li><p>A <code>lookup-expression</code> takes the form <code>E1?K</code>, where <code>E1</code> is an expression returning a sequence of maps or arrays, and <code>K</code> is a key specifier, which indicates which entries in a map, or members in an array, should be selected.</p><p>Lookup expressions are described in <a href="#id-postfix-lookup"><b>4.14.3.1 Postfix Lookup Expressions</b></a>.</p><p>An example of a lookup expression is <code>$emp?name</code>, where the value of variable <code>$emp</code> is a map, and the string <code>"name"</code> is the key of one of the entries in the map.</p></li></ul><p>Postfix expressions are evaluated from left-to-right. For example, the expression <code>$E1[E2]?(E3)(E4)</code> is evaluated by first evaluating the filter expression <code>$E1[E2]</code> to produce a sequence of maps and arrays (say <code>$S</code>), then evaluating the lookup expression <code>$S?(E3)</code> to produce a function item (say <code>$F</code>), then evaluating the dynamic function call <code>$F(E4)</code> to produce the final result.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>The grammar for postfix expressions is defined here in a way designed to link clearly to the semantics of the different kinds of expression. For parsing purposes, the equivalent production rule:</p><div class="exampleInner"><pre xml:space="preserve">PostfixExpr := PrimaryExpr (Predicate | PositionalArgumentList | Lookup)*</pre></div><p>(as used in XPath 3.1) is probably more convenient.</p></div></div><div class="div2"><h3><a id="id-filter-expression"></a>4.4 Filter Expressions</h3><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-function-calls">⬇</a>&nbsp;<a href="#id-numeric-literals">⬆</a></p><ol><li><p> The value of a predicate in a filter expression can now be a sequence of integers. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/816">816</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/996">996</a>&nbsp;6 February 2024]</i></p></li></ol></div><a id="d3e15901"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-FilterExpr"></a><code><a href="#prod-xquery40-FilterExpr">FilterExpr</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-PostfixExpr">PostfixExpr</a><a href="#doc-xquery40-Predicate">Predicate</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-Predicate"></a><code><a href="#prod-xquery40-Predicate">Predicate</a></code></td><td>::=</td><td><code>"[" <a href="#doc-xquery40-Expr">Expr</a> "]"</code></td></tr></tbody></table><p>A filter expression consists of a base expression followed by a predicate, which is an expression written in square brackets. The result of the filter expression consists of the items returned by the base expression, filtered by applying the predicate to each item in turn. The ordering of the items returned by a filter expression is the same as their order in the result of the primary expression.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>Where the expression before the square brackets is a <a href="#doc-xquery40-ReverseStep">ReverseStep</a> or <a href="#doc-xquery40-ForwardStep">ForwardStep</a>, the expression is technically not a filter expression but an <a href="#doc-xquery40-AxisStep">AxisStep</a>. There are minor differences in the semantics: see <a href="#id-predicate"><b>4.6.5 Predicates within Steps</b></a></p></div><p>Here are some examples of filter expressions:</p><ul><li><p>Given a sequence of products in a variable, return only those products whose price is greater than 100.</p><div class="exampleInner"><pre xml:space="preserve">$products[price gt 100]</pre></div></li><li><p>List all the integers from 1 to 100 that are divisible by 5. (See <a href="#construct_seq"><b>4.7.1 Sequence Concatenation</b></a> for an explanation of the <code>to</code> operator.)</p><div class="exampleInner"><pre xml:space="preserve">(1 to 100)[. mod 5 eq 0]</pre></div></li><li><p>The result of the following expression is the integer 25:</p><div class="exampleInner"><pre xml:space="preserve">(21 to 29)[5]</pre></div></li><li><p>The following example returns the fifth through ninth items in the sequence bound to variable <code>$orders</code>.</p><div class="exampleInner"><pre xml:space="preserve">$orders[5 to 9]</pre></div></li><li><p>The following example illustrates the use of a filter expression as a <a title="step" class="termref" href="#dt-step">step</a> in a <a title="path expression" class="termref" href="#dt-path-expression">path expression</a>. It returns the last chapter or appendix within the book bound to variable <code>$book</code>:</p><div class="exampleInner"><pre xml:space="preserve">$book/(chapter | appendix)[last()]</pre></div></li></ul><p>For each item in the input sequence, the predicate expression is evaluated using an <b>inner focus</b>, defined as follows: The context value is the item currently being tested against the predicate. The context size is the number of items in the input sequence. The context position is the position of the context value within the input sequence. </p><p>For each item in the input sequence, the result of the predicate expression is coerced to an <code>xs:boolean</code> value, called the <a title="predicate truth value" class="termref" href="#dt-predicate-truth-value">predicate truth value</a>, as described below. Those items for which the predicate truth value is <code>true</code> are retained, and those for which the predicate truth value is <code>false</code> are discarded.</p><p> [<a id="dt-predicate-truth-value" title="predicate truth value">Definition</a>: The <b>predicate truth value</b> of a value <code>$V</code> is the result of the expression <code>if ($V instance of xs:numeric+) then ($V = position()) else fn:boolean($V)</code>.] </p><p>Expanding this definition, the predicate truth value can be obtained by applying the following rules, in order:</p><ol class="enumar"><li><p>If the value <var>V</var> of the predicate expression is a sequence whose first item is an instance of the type <code>xs:numeric</code>, then:</p><ol class="enumla"><li><p><var>V</var> must be an instance of the type <code>xs:numeric+</code> (that is, every item in <var>V</var> must be numeric). A type error [<a href="https://qt4cg.org/specifications/xpath-functions-40/#ERRFORG0006" title="err:FORG0006">err:FORG0006</a>]<sup><small>FO40</small></sup> is raised if this is not the case.</p></li><li><p>The predicate truth value is <code>true</code> if <var>V</var> is equal (by the <code>=</code> operator) to the <b>context position</b>, and is <code>false</code> otherwise.</p></li></ol><p>In effect this means that an item in the input sequence is selected if its position in the sequence is equal to one or more of the numeric values in the predicate. For example, the predicate <code>[3 to 5]</code> is true for the third, fourth, and fifth items in the input sequence.</p><p> [<a id="dt-numeric-predicate" title="numeric predicate">Definition</a>: A predicate whose predicate expression returns a value of type <code>xs:numeric+</code> is called a <b>numeric predicate</b>.] </p><div class="note"><p class="prefix"><b>Note:</b></p><p>It is possible, though not generally useful, for the value of a numeric predicate to depend on the focus, and thus to differ for different items in the input sequence. For example, the predicate <code>[xs:integer(@seq)]</code> selects those items in the input sequence whose <code>@seq</code> attribute is numerically equal to their position in the input sequence.</p><p>It is also possible, and again not generally useful, for the value of the predicate to be numeric for some items in the input sequence, and boolean for others. For example, the predicate <code>[@special otherwise last()]</code> is true for an item that either has an <code>@special</code> attribute, or is the last item in the input sequence.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The truth value of a numeric predicate does not depend on the order of the numbers in <var>V</var>. The predicates <code>[ 1, 2, 3 ]</code> and <code>[ 3, 2, 1 ]</code> have exactly the same effect. The items in the result of a filter expression always retain the ordering of the input sequence.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>The truth value of a numeric predicate whose value is non-integral or non-positive is always false.</p></div><div class="note"><p class="prefix"><b>Note:</b></p><p>Beware that using boolean operators (<code>and</code>, <code>or</code>, <code>not()</code>) with numeric values may not have the intended effect. For example the predicate <code>[1 or last()]</code> selects every item in the sequence, because <code>or</code> operates on the <a title="effective boolean value" class="termref" href="#dt-ebv">effective boolean value</a> of its operands. The required effect can be achieved with the predicate <code>[1, last()]</code>.</p></div></li><li><p>Otherwise, the predicate truth value is the <a title="effective boolean value" class="termref" href="#dt-ebv">effective boolean value</a> of the predicate expression.</p></li></ol></div><div class="div2"><h3><a id="id-functions"></a>4.5 Functions</h3><p>Functions in XQuery 4.0 arise in two ways:</p><ul><li><p>A <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> contains information about a family of functions with the same name and a defined arity range. These functions are in most cases known statically (they appear in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a>), but there may be further function definitions that are known only dynamically (appearing in the <a title="dynamically known function definitions" class="termref" href="#dt-dynamically-known-function-definitions">dynamically known function definitions</a>).</p></li><li><p><a title="function item" class="termref" href="#dt-function-item">Function items</a> are XDM items that can be called using a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-call">dynamic function call</a>. They are values that can be bound to variables, passed as arguments, returned as function results, and generally manipulated in the same way as other XDM values.</p></li></ul><p>The functions defined by a statically known <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> can be invoked using a <a title="static function call" class="termref" href="#dt-static-function-call">static function call</a>. <a title="function item" class="termref" href="#dt-function-item">Function items</a> corresponding to these definitions can also be obtained, as dynamic values, by evaluating a <a title="named function reference" class="termref" href="#dt-named-function-ref">named function reference</a>. <a title="function item" class="termref" href="#dt-function-item">Function items</a> can also be obtained using the <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-function-lookup"><code>fn:function-lookup</code></a> function: in this case the function name and arity do not need to be known statically, and the function definition need not be present in the <a title="static context" class="termref" href="#dt-static-context">static context</a>, so long as it is in the <a title="dynamic context" class="termref" href="#dt-dynamic-context">dynamic context</a>.</p><p>Static and dynamic function calls are described in the following sections.</p><div class="div3"><h4><a id="id-static-functions"></a>4.5.1 Static Function Calls</h4><p>The <a title="static context" class="termref" href="#dt-static-context">static context</a> for an expression includes a set of <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a>. Every <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context has a name (which is an <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a>) and an <a title="arity range" class="termref" href="#dt-arity-range">arity range</a>, which is a range of permitted arities for calls on that function. Two <a title="function definition" class="termref" href="#dt-function-definition">function definitions</a> having the same name must not have overlapping arity ranges. This means that for a given static function call, it is possible to identify the target function definition in the static context unambiguously from knowledge of the function name and the number of supplied arguments.</p><p>A <a title="static function call" class="termref" href="#dt-static-function-call">static function call</a> is bound to a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context by matching the name and arity. If the function call has <var>P</var> positional arguments followed by <var>K</var> keyword arguments, then the required arity is <var>P+K</var>, and the static context must include a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> whose name matches the <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a> in the function call, and whose <a title="arity range" class="termref" href="#dt-arity-range">arity range</a> includes this required arity. This is the function chosen to be called. The result of the function is obtained by evaluating the expression that forms its implementation, with a dynamic context that provides values for all the declared parameters, initialized as described in <a href="#id-eval-static-function-call"><b>4.5.1.2 Evaluating Static Function Calls</b></a> below.</p><p>Similarly, a function reference of the form <code>f#N</code> binds to a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the static context whose name matches <var>f</var> where <code>MinP ≤ N and MaxP ≥ N</code>. The result of evaluating a function reference is a <a title="function item" class="termref" href="#dt-function-item">function item</a> which can be called using a dynamic function call. Function items are never variadic and their arguments are always supplied positionally. For example, the function reference <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-concat"><code>fn:concat#3</code></a> returns a function item with arity 3, which is always called by supplying three positional arguments, and whose effect is the same as a static call on <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-concat"><code>fn:concat</code></a> with three positional arguments. </p><p>The detailed rules for evaluating static function calls and function references are defined in subsequent sections.</p><div class="div4"><h5><a id="id-function-calls"></a>4.5.1.1 Static Function Call Syntax</h5><div class="changes"><p class="changesHeading">Changes in 4.0&nbsp;<a href="#id-inline-func">⬇</a>&nbsp;<a href="#id-filter-expression">⬆</a></p><ol><li><p> Keyword arguments are allowed on static function calls, as well as positional arguments. <i>&nbsp;&nbsp;[Issue <a href="https://github.com/qt4cg/qtspecs/issues/155">155</a>&nbsp;PR <a href="https://github.com/qt4cg/qtspecs/pull/159">159</a>&nbsp;30 September 2020]</i></p></li></ol></div><a id="d3e16234"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-FunctionCall"></a><code><a href="#prod-xquery40-FunctionCall">FunctionCall</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-EQName">EQName</a><a href="#doc-xquery40-ArgumentList">ArgumentList</a></code></td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-reserved-function-names">xgc: reserved-function-names</a> */</td></tr><tr><td></td><td></td><td style="text-align: right;" class="prodComment">/* <a href="#parse-note-parens">gn: parens</a> */</td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-ArgumentList"></a><code><a href="#prod-xquery40-ArgumentList">ArgumentList</a></code></td><td>::=</td><td><code>"(" ((<a href="#doc-xquery40-PositionalArguments">PositionalArguments</a> ("," <a href="#prod-xquery40-KeywordArguments">KeywordArguments</a>)?) | <a href="#prod-xquery40-KeywordArguments">KeywordArguments</a>)? ")"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e15060.doc-xquery40-PositionalArguments"></a><code>PositionalArguments</code></td><td>::=</td><td><code>(<a href="#doc-xquery40-Argument">Argument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-Argument"></a><code><a href="#prod-xquery40-Argument">Argument</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-ExprSingle">ExprSingle</a> | <a href="#doc-xquery40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-ArgumentPlaceholder"></a><code><a href="#prod-xquery40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td><td>::=</td><td><code>"?"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e15063.doc-xquery40-KeywordArguments"></a><code>KeywordArguments</code></td><td>::=</td><td><code>(<a href="#doc-xquery40-KeywordArgument">KeywordArgument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-KeywordArgument"></a><code><a href="#prod-xquery40-KeywordArgument">KeywordArgument</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-EQName">EQName</a> ":=" <a href="#doc-xquery40-Argument">Argument</a></code></td></tr></tbody></table><p> [<a id="dt-static-function-call" title="static function call">Definition</a>: A <b>static function call</b> consists of an EQName followed by a parenthesized list of zero or more arguments.] </p><p>The argument list consists of zero or more positional arguments, followed by zero or more keyword arguments.</p><p> [<a id="dt-arg-expr" title="argument expression">Definition</a>: An argument to a function call is either an <b>argument expression</b> or an <a href="#doc-xquery40-ArgumentPlaceholder">ArgumentPlaceholder</a> (<code>?</code>); in both cases it may either be supplied positionally, or identified by a name (called a keyword).] </p><p>This section is concerned with static function calls in which none of the arguments are <a href="#doc-xquery40-ArgumentPlaceholder">ArgumentPlaceholders</a>. Calls using one or more <a href="#doc-xquery40-ArgumentPlaceholder">ArgumentPlaceholders</a> are covered in the section <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p>If the function name supplied in a static function call is an unprefixed <a title="lexical QName" class="termref" href="#dt-qname">lexical QName</a>, it is expanded using the <a title="default function namespace" class="termref" href="#dt-default-function-namespace">default function namespace</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a>. </p><p> The <a title="expanded QName" class="termref" href="#dt-expanded-qname">expanded QName</a> used as the function name and the number of arguments used in the static function call (the required arity) must match the name and arity range of a <a title="function definition" class="termref" href="#dt-function-definition">function definition</a> in the <a title="static context" class="termref" href="#dt-static-context">static context</a><span> using the rules defined in the previous section</span>; if there is no match, a <a title="static error" class="termref" href="#dt-static-error">static error</a> is raised [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>]. </p><p>Evaluation of static function calls is described in <a href="#id-eval-static-function-call"><b>4.5.1.2 Evaluating Static Function Calls</b></a> .</p><p>Since the arguments of a function call are separated by commas, any <a title="argument expression" class="termref" href="#dt-arg-expr">argument expression</a> that contains a top-level <a title="comma operator" class="termref" href="#dt-comma-operator">comma operator</a> must be enclosed in parentheses. Here are some illustrative examples of static function calls:</p><ul><li><p><code>my:three-argument-function(1, 2, 3)</code> denotes a static function call with three <span>positional</span> arguments. <span>The corresponding function declaration must define at least three parameters, and may define more, provided they are optional.</span></p></li><li><p><code>my:two-argument-function((1, 2), 3)</code> denotes a static function call with two arguments, the first of which is a sequence of two values. <span>The corresponding function declaration must define at least two parameters, and may define more, provided they are optional.</span></p></li><li><p><code>my:two-argument-function(1, ())</code> denotes a static function call with two arguments, the second of which is an empty sequence.</p></li><li><p><code>my:one-argument-function((1, 2, 3))</code> denotes a static function call with one argument that is a sequence of three values. </p></li><li><p><code>my:one-argument-function(( ))</code> denotes a static function call with one argument that is an empty sequence.</p></li><li><p><code>my:zero-argument-function( )</code> denotes a static function call with zero arguments.</p></li><li><p><code>lang(node := $n, language := 'de')</code> is a static function call with two keyword arguments. The corresponding function declaration defines two parameters, a required parameter <code>language</code> and an optional parameter <code>node</code>. This call supplies values for both parameters. It is equivalent to the call <code>fn:lang('de', $n)</code>. Note that the keyword arguments are in a different order from the parameter declarations. </p></li><li><p><code>sort(//employee, key := fn($e) { xs:decimal($e/salary) })</code> is a static function call with one positional argument and one keyword argument. The corresponding function declaration defines three parameters, a required parameter <code>$input</code>, an optional parameter <code>$collation</code>, and an optional parameter <code>$key</code> This call supplies values for the first and third parameters, leaving the second parameter (<code>$collation</code>) to take its default value. The default value of the <code>$collation</code> parameter is given as <code>fn:default-collation()</code>, so the value supplied to the function is the default collation from the dynamic context of the caller. It is equivalent to the call <code>fn:sort(//employee, fn:default-collation(), fn($e) { xs:decimal($e/salary) })</code>. </p></li></ul><p>An <code>EQName</code> in a <code>KeywordArgument</code> is expanded to a QName value; if there is no prefix, then the name is in no namespace (otherwise the prefix is resolved in the usual way). The keywords used in a function call (after expansion to QNames) must be distinct [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>]; [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>].</p></div><div class="div4"><h5><a id="id-eval-static-function-call"></a>4.5.1.2 Evaluating Static Function Calls</h5><p>This section applies to static function calls where none of the arguments is an <code>ArgumentPlaceholder</code>. For function calls involving placeholders, see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p> When a static function call <var>FC</var> is evaluated with respect to a static context <var>SC</var> and a dynamic context <var>DC</var>, the result is obtained as follows: </p><ol class="enumar"><li><p> The <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> to be used is found in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a> of <var>SC</var>. </p><p>The <b>required arity</b> is the total number of arguments in the function call, including both positional and keyword arguments.</p><p> There can be at most one <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> in the <a title="statically known function definitions" class="termref" href="#dt-statically-known-function-definitions">statically known function definitions</a> component of <var>SC</var> whose function name matches the expanded QName in <var>FC</var> and whose <a title="arity range" class="termref" href="#dt-arity-range">arity range</a> includes the arity of <var>FC</var>’s <code>ArgumentList</code>. </p><p>If there is no such <a title="function definition" class="termref" href="#dt-function-definition">function definition</a>, a static error [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>] is raised.</p></li><li><p>Each parameter in the <a title="function definition" class="termref" href="#dt-function-definition">function definition</a><var>FD</var> is matched to an argument expression as follows:</p><ol class="enumla"><li><p>If there are <var>N</var> positional arguments in the function call <var>FC</var>, then the corresponding argument expressions are matched pairwise to the first <var>N</var> parameters in the declaration. For this purpose the required parameters and optional parameters in <var>FD</var> are concatenated into a single list, in order.</p></li><li><p>Any keyword arguments in <var>FC</var> are then matched to parameters (whether required or optional) in <var>FD</var> by comparing the keyword used in <var>FC</var> with the paramater name declared in <var>FD</var>. Each keyword must match the name of a declared parameter [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>], and this must be one that has not already been matched to a positional argument. [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>].</p></li><li><p>If any required parameter has not been matched to any argument in <var>FC</var> by applying the above rules, a static error is reported [<a href="#ERRXPST0017" title="err:XPST0017">err:XPST0017</a>] </p></li><li><p>If any optional parameter has not been matched to any argument in <var>FC</var> by applying the above rules, then the parameter is matched to the default value expression for that parameter in <var>FD</var>.</p></li></ol></li><li><p> Each argument expression established by the above rules is evaluated with respect to DC. The order of argument evaluation is <a title="implementation   dependent" class="termref" href="#dt-implementation-dependent">implementation dependent</a> and it is not required that an argument be evaluated if the function body can be evaluated without evaluating that argument.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>All argument expressions, including default value expressions, are evaluated in the dynamic context of the function call. It is therefore possible to use a default value expression such as <code>.</code>, or <code>/</code>, or <code>fn:current-dateTime()</code>, whose value depends on the dynamic context of the function call.</p></div><p>If the expression used for the default value of a parameter has no dependencies on the dynamic context, then an implementation <span class="verb">may</span> choose to reuse the same value on repeated function calls rather than re-evaluating it on each function call.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>This is relevant, for example, if the expression constructs new nodes.</p></div></li><li><p>The result of evaluating the argument expression is converted to the required type (the declared type associated with the corresponding parameter in the function declaration, defaulting to <code>item()*</code>) by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>.</p><p><span>This applies both to explicitly supplied arguments, and to values obtained by evaluating default value expressions. In both cases a type error will be raised if the value (after coercion) does not match the required type.</span></p></li><li><p>The result of the function call is obtained as follows:</p><ul><li><p><var>FD</var>’s <span>body</span> is invoked in an implementation-dependent way. The processor makes the following information available to that invocation: </p><ul><li><p>The converted argument values;</p></li><li><p>If the function is <a title="context dependent" class="termref" href="#dt-context-dependent">context dependent</a>, the static context <var>SC</var> and dynamic context <var>DC</var> of the function call. </p></li></ul></li><li><p>The result is converted to the required type (the declared return type in the function declaration, defaulting to <code>item()*</code>) by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>.</p><p>The result of applying the coercion rules is either an instance of <var>FD</var>’s return type or a dynamic error. This result is then the result of evaluating <var>FC</var>.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>A host language may define alternative rules for processing the result, especially in the case of external functions implemented using a non-XDM type system.</p></div></li><li><p> Errors raised by system functions are defined in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>. </p></li><li class="xquery"><p> Errors raised by external functions are <a title="implementation defined" class="termref" href="#dt-implementation-defined">implementation-defined</a> (see <a href="#id-consistency-constraints"><b>2.3.6 Consistency Constraints</b></a>). </p></li></ul><div class="example"><div class="exampleHeader"><a id="d3e16696"></a>Example: A System Function</div><p>The following function call uses the function <a href="https://qt4cg.org/specifications/xpath-functions-40/#func-base-uri">Section 2.1.5 fn:base-uri</a><sup><small>FO</small></sup>. Use of <code>SC</code> and <code>DC</code> and errors raised by this function are all defined in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>.</p><div class="exampleInner"><pre xml:space="preserve">base-uri()</pre></div></div></li></ol></div></div><div class="div3"><h4><a id="id-dynamic-functions"></a>4.5.2 Function Items</h4><p>A <a title="function item" class="termref" href="#dt-function-item">function item</a> is an XDM value that can be bound to a variable, or manipulated in various ways by XQuery 4.0 expressions. The most significant such expression is a <a title="dynamic function call" class="termref" href="#dt-dynamic-function-call">dynamic function call</a>, which supplies values of arguments and evaluates the function to produce a result.</p><p>The syntax of dynamic function calls is defined in <a href="#id-dynamic-function-invocation"><b>4.5.2.1 Dynamic Function Calls</b></a>.</p><p>A number of constructs can be used to produce a <a title="function item" class="termref" href="#dt-function-item">function item</a>, notably:</p><ul><li><p>A <b>named function reference</b> (see <a href="#id-named-function-ref"><b>4.5.2.4 Named Function References</b></a>) constructs a function item by reference to <a title="function definition" class="termref" href="#dt-function-definition">function definitions</a> in the static context. For example, <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-node-name"><code>fn:node-name#1</code></a> returns a function item whose effect is to call the static <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-node-name"><code>fn:node-name</code></a> function with one argument.</p></li><li><p>An <b>inline function</b> (see <a href="#id-inline-func"><b>4.5.2.5 Inline Function Expressions</b></a> ) constructs a function item whose <span>body</span> is defined locally. For example, the construct <code>fn($x) { $x + 1 }</code> returns a function item whose effect is to increment the value of the supplied argument.</p></li><li><p>A <b>partial function application</b> (see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>) derives one function item from another by supplying the values of some of its arguments. For example, <code>fn:ends-with(?, ".txt")</code> returns a function item with one argument that tests whether the supplied string ends with the substring <code>".txt"</code>.</p></li><li><p>Maps and arrays are also function items. See <a href="#id-map-constructors"><b>4.14.1.1 Map Constructors</b></a> and <a href="#id-array-constructors"><b>4.14.2.1 Array Constructors</b></a>.</p></li><li><p>The <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-function-lookup"><code>fn:function-lookup</code></a> function can be called to discover functions that are present in the <a title="dynamic context" class="termref" href="#dt-dynamic-context">dynamic context</a>.</p></li><li><p>The <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-load-xquery-module"><code>fn:load-xquery-module</code></a> function can be called to load functions dynamically from an external XQuery library module.</p></li><li><p>Some system functions such as <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-random-number-generator"><code>fn:random-number-generator</code></a> and <a href="https://qt4cg.org/specifications/xpath-functions-40/Overview.html#func-op"><code>fn:op</code></a> return a <a title="function item" class="termref" href="#dt-function-item">function item</a> as their result.</p></li></ul><p>These constructs are described in detail in the following sections, or in <a href="#xpath-functions-40">[XQuery and XPath Functions and Operators 4.0]</a>.</p><div class="div4"><h5><a id="id-dynamic-function-invocation"></a>4.5.2.1 Dynamic Function Calls</h5><a id="d3e16805"></a><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-DynamicFunctionCall"></a><code><a href="#prod-xquery40-DynamicFunctionCall">DynamicFunctionCall</a></code></td><td>::=</td><td><code><a href="#doc-xquery40-PostfixExpr">PostfixExpr</a><a href="#doc-xquery40-PositionalArgumentList">PositionalArgumentList</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-PositionalArgumentList"></a><code><a href="#prod-xquery40-PositionalArgumentList">PositionalArgumentList</a></code></td><td>::=</td><td><code>"(" <a href="#doc-xquery40-PositionalArguments">PositionalArguments</a>? ")"</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-PositionalArguments"></a><code><a href="#prod-xquery40-PositionalArguments">PositionalArguments</a></code></td><td>::=</td><td><code>(<a href="#doc-xquery40-Argument">Argument</a> ++ ",")</code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e15569.doc-xquery40-Argument"></a><code>Argument</code></td><td>::=</td><td><code><a href="#doc-xquery40-ExprSingle">ExprSingle</a> | <a href="#doc-xquery40-ArgumentPlaceholder">ArgumentPlaceholder</a></code></td></tr></tbody><tbody><tr style="vertical-align:baseline;"><td><a id="noid_d4e15570.doc-xquery40-ArgumentPlaceholder"></a><code>ArgumentPlaceholder</code></td><td>::=</td><td><code>"?"</code></td></tr></tbody></table><p> [<a id="dt-dynamic-function-invocation" title="dynamic function call">Definition</a>: A <b>dynamic function call</b> consists of a base expression that returns the function and a parenthesized list of zero or more arguments (<a title="argument expression" class="termref" href="#dt-arg-expr">argument expressions</a> or ArgumentPlaceholders).] </p><p> A dynamic function call is evaluated as described in <a href="#id-eval-dynamic-function-call"><b>4.5.2.2 Evaluating Dynamic Function Calls</b></a>. </p><p>The following are examples of some dynamic function calls:</p><ul><li><p>This example calls the function contained in <code>$f</code>, passing the arguments 2 and 3: </p><div class="exampleInner"><pre xml:space="preserve">$f(2, 3)</pre></div></li><li><p>This example fetches the second item from sequence <code>$f</code>, treats it as a function and calls it, passing an <code>xs:string</code> argument: </p><div class="exampleInner"><pre xml:space="preserve">$f[2]("Hi there")</pre></div></li><li><p>This example calls the function <code>$f</code> passing no arguments, and filters the result with a positional predicate: </p><div class="exampleInner"><pre xml:space="preserve">$f()[2]</pre></div></li></ul><div class="note"><p class="prefix"><b>Note:</b></p><p>Arguments in a dynamic function call are always supplied positionally.</p></div></div><div class="div4"><h5><a id="id-eval-dynamic-function-call"></a>4.5.2.2 Evaluating Dynamic Function Calls</h5><p>This section applies to dynamic function calls whose arguments do not include an <code>ArgumentPlaceholder</code>. For function calls that include a placeholder, see <a href="#id-partial-function-application"><b>4.5.2.3 Partial Function Application</b></a>.</p><p> [<a id="dt-dynamic-function-call" title="dynamic function call">Definition</a>: A <b>dynamic function call</b> is an expression that is evaluated by calling a <a title="function item" class="termref" href="#dt-function-item">function item</a>, which is typically obtained dynamically.] </p><p> When a dynamic function call <var>FC</var> is evaluated, the result is obtained as follows: </p><ol class="enumar"><li><p> The <a title="function item" class="termref" href="#dt-function-item">function item</a><var>FI</var> to be called is obtained by evaluating the base expression of the function call. If this yields a sequence consisting of a single function item whose arity matches the number of arguments in the <code>ArgumentList</code>, let <var>FI</var> denote that function item. Otherwise, a type error is raised [<a href="#ERRXPTY0004" title="err:XPTY0004">err:XPTY0004</a>]. </p><div class="note"><p class="prefix"><b>Note:</b></p><p>Keyword arguments are not allowed in a dynamic function call.</p></div></li><li><p><a title="argument expression" class="termref" href="#dt-arg-expr">Argument expressions</a> are evaluated, producing <b>argument values</b>. The order of argument evaluation is <a title="implementation   dependent" class="termref" href="#dt-implementation-dependent">implementation-dependent</a> and an argument need not be evaluated if the function body can be evaluated without evaluating that argument.</p></li><li><p> Each argument value is converted to the corresponding parameter type in <var>FI</var>’s signature by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>, resulting in a <b>converted argument value</b></p></li><li><p>If <var>FI</var> is a map, it is evaluated as described in <a href="#id-map-lookup"><b>4.14.1.2 Maps as Functions</b></a>.</p></li><li><p>If <var>FI</var> is an array, it is evaluated as described in <a href="#id-array-lookup"><b>4.14.2.2 Arrays as Functions</b></a>.</p></li><li><p> If <var>FI</var>’s <span>body</span> is an XQuery 4.0 expression (for example, if <var>FI</var> is <span class="xquery">a <a title="user-defined function" class="termref" href="#dt-udf">user-defined function</a> or</span> an <a title="anonymous function" class="termref" href="#dt-anonymous-function">anonymous function</a>, or a <a title="partially applied function" class="termref" href="#dt-partially-applied-function">partial application</a> of such a function): </p><ol class="enumla"><li><p><var>FI</var>’s <span>body</span> is evaluated. The static context for this evaluation is the static context of the XQuery 4.0 expression. The dynamic context for this evaluation is obtained by taking the dynamic context of the <span class="xquery">module</span> that contains the <code>FunctionBody</code>, and making the following changes: </p><ul><li><p> The <a title="focus" class="termref" href="#dt-focus">focus</a> (context value, context position, and context size) is <a href="https://qt4cg.org/specifications/xpath-datamodel-40/#dt-absent">absent</a><sup><small>DM</small></sup>. </p></li><li><p> In the <a title="variable values" class="termref" href="#dt-variable-values">variable values</a> component of the dynamic context, each converted argument value is bound to the corresponding parameter name. </p><p><span>When this is done, the converted argument values retain their <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic types</a>, even where these are <a title="subtype" class="termref" href="#dt-subtype">subtypes</a> of the declared parameter types.</span> For example, a function with a parameter <code>$p</code> of type <code>xs:decimal</code> can be called with an argument of type <code>xs:integer</code>, which is derived from <code>xs:decimal</code>. During the processing of this function call, the value of <code>$p</code> inside the body of the function retains its <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic type</a> of <code>xs:integer</code>. </p></li><li><p><var>FI</var>’s nonlocal variable bindings are also added to the <a title="variable values" class="termref" href="#dt-variable-values">variable values</a>. (Note that the names of the nonlocal variables are by definition disjoint from the parameter names, so there can be no conflict.) </p></li></ul></li><li><p> The value returned by evaluating the function body is then converted to the declared return type of <var>FI</var> by applying the <a title="coercion rules" class="termref" href="#dt-coercion-rules">coercion rules</a>. The result is then the result of evaluating <var>FC</var>. </p><p> As with argument values, the value returned by a function retains its <a title="dynamic type" class="termref" href="#dt-dynamic-type">dynamic type</a>, which may be a <a title="subtype" class="termref" href="#dt-subtype">subtype</a> of the declared return type of <var>FI</var>. For example, a function that has a declared return type of <code>xs:decimal</code> may in fact return a value of dynamic type <code>xs:integer</code>. </p></li></ol><div class="example"><div class="exampleHeader"><a id="d3e17083"></a>Example: Derived Types and Nonlocal Variable Bindings</div><p><code>$incr</code> is a nonlocal variable that is available within the function because its variable binding has been added to the variable values of the function.. Even though the parameter and return type of this function are both <code>xs:decimal</code>, the more specific type <code>xs:integer</code> is preserved in both cases.</p><div class="exampleInner"><pre xml:space="preserve">let $incr := 1
 let $f := function($i as xs:decimal) as xs:decimal { $i + $incr }
 return $f(5)</pre></div></div><p>&nbsp;</p><div class="example"><div class="exampleHeader"><a id="d3e17098"></a>Example: Using the Context Value in an Anonymous Function</div><p>The following example will raise a <a title="type error" class="termref" href="#dt-type-error">type error</a> [<a href="#ERRXPDY0002" title="err:XPDY0002">err:XPDY0002</a>]:</p><div class="exampleInner"><pre xml:space="preserve">let $vat := function() { @vat + @price }
 return doc('wares.xml')/shop/article/$vat()</pre></div><p>Instead, the context value can be used as an argument to the anonymous function:</p><div class="exampleInner"><pre xml:space="preserve">let $vat := function($art) { $art/@vat + $art/@price }
diff --git a/pr/1686/xquery-40/xquery-40-diff.html b/pr/1686/xquery-40/xquery-40-diff.html
index 2a0573d9a..76ec9f0e5 100644
--- a/pr/1686/xquery-40/xquery-40-diff.html
+++ b/pr/1686/xquery-40/xquery-40-diff.html
@@ -9211,7 +9211,7 @@ <h2><a id="id-expressions"></a>4 Expressions</h2>
             <a href="#doc-xquery40-IfExpr">IfExpr</a>,
 <span class="xquery">
                <a href="#doc-xquery40-TryCatchExpr">TryCatchExpr</a>, </span>
-and <a href="#doc-xquery40-OrExpr">OrExpr</a>. Each of these expressions is described in a separate section of this document.</p>
+and <a href="#doc-xquery40-PipelineExpr">PipelineExpr</a>. Each of these expressions is described in a separate section of this document.</p>
             <div class="div2">
                
                <h3><a id="comments"></a>4.1 Comments</h3>
diff --git a/pr/1686/xquery-40/xquery-40.html b/pr/1686/xquery-40/xquery-40.html
index 0fd650673..5584eccfa 100644
--- a/pr/1686/xquery-40/xquery-40.html
+++ b/pr/1686/xquery-40/xquery-40.html
@@ -8983,7 +8983,7 @@ <h2><a id="id-expressions"></a>4 Expressions</h2>
             <a href="#doc-xquery40-IfExpr">IfExpr</a>,
 <span class="xquery">
                <a href="#doc-xquery40-TryCatchExpr">TryCatchExpr</a>, </span>
-and <a href="#doc-xquery40-OrExpr">OrExpr</a>. Each of these expressions is described in a separate section of this document.</p>
+and <a href="#doc-xquery40-PipelineExpr">PipelineExpr</a>. Each of these expressions is described in a separate section of this document.</p>
             <div class="div2">
                
                <h3><a id="comments"></a>4.1 Comments</h3>
diff --git a/pr/1686/xquery-40/xquery-40.xml b/pr/1686/xquery-40/xquery-40.xml
index 7d3a5072a..18fd68669 100644
--- a/pr/1686/xquery-40/xquery-40.xml
+++ b/pr/1686/xquery-40/xquery-40.xml
@@ -4213,7 +4213,7 @@ return $f(12.3)</pre></div><p class="xquery">With XQuery 4.0, as a consequence o
             <a href="#doc-xquery40-IfExpr">IfExpr</a>,
 <span class="xquery">
                <a href="#doc-xquery40-TryCatchExpr">TryCatchExpr</a>, </span>
-and <a href="#doc-xquery40-OrExpr">OrExpr</a>. Each of these expressions is described in a separate section of this document.</p><div class="div2">
+and <a href="#doc-xquery40-PipelineExpr">PipelineExpr</a>. Each of these expressions is described in a separate section of this document.</p><div class="div2">
 <h3><a id="comments"/>4.1 Comments</h3>
 <a id="d3e14566"/><table class="scrap"><tbody><tr style="vertical-align:baseline;"><td><a id="doc-xquery40-Comment"/><code><a href="#prod-xquery40-Comment">Comment</a></code></td><td>::=</td><td><code>"(:"  (<a href="#doc-xquery40-CommentContents">CommentContents</a>  |  <a href="#doc-xquery40-Comment">Comment</a>)*  ":)"</code></td></tr><tr><td/><td/><td style="text-align: right;" class="prodComment">/* 
                      <a href="#ws-explicit">ws: explicit</a>

Supplied Value	Coercion
`"[0-9]"`	None; the supplied value is an instance of the required type.
`default-language()`	None; the supplied value is an instance of `xs:language`, which is a subtype of the required type `xs:string`.
`<a>[0-9]</a>`	The supplied element node is atomized. Unless it has been schema-validated, the typed value will be an instance of `xs:untypedAtomic`, which is accepted when the required type is `xs:string`. Supplying an element whose type annotation is (say) `xs:date` will fail with a type error. The effect is subtly different if XPath 1.0 compatibility mode is enabled. In this case coercion takes the string value of the element node. This differs from the typed value only in the case where the element has been schema-validated and has a type annotation other than `xs:string`.
`xs:anyURI("urn:dummy")`	Supplying an instance of `xs:anyURI` where the expected type is `xs:string` is permitted; this is one of the pairs of types where implicit casting is allowed.
`17.2`	Supplying a number where a string is expected raises a type error. However, if XPath 1.0 compatibility mode is enabled, the number is converted to a string as if by the `fn:string` function.
`//author/@id`	Supplying a sequence of nodes where a single string is expected will raise a type error unless either there is only one node in the sequence. In this case the typed value of the node will be used (this must be of type `xs:string`, `xs:untypedAtomic`, or `xs:anyURI`). If XPath 1.0 compatibility mode is enabled, however, all strings after the first are discarded, and the string value of the first node is used; if the sequence is empty, a zero-length string is supplied.
`("red", "green", "blue")`	Supplying a sequence of strings where a single string is expected raises a type error. If XPath 1.0 compatibility mode is enabled, however, all strings after the first are discarded; the effect is as if the supplied value were `"red"`.
`()`	Supplying an empty sequence where a single string is expected will fail. If XPath 1.0 compatibility mode is enabled, however, the value is coerced by applying the function `fn:string(())`, which delivers the zero-length string.
`["a\|b"]`	Supplying an array holding a single string succeeds, because the rules cause the array to be atomized, and the value after atomization is a single string. Supplying an array holding multiple strings would fail. In XPath 1.0 compatibility mode, supplying an array will fail, regardless of the array contents, because the `fn:string` function does not accept arrays.
Supplied Value	Coercion
`12.4`	None; the supplied value is an instance of the required type.
`()`	None; an empty sequence is an instance of the required type.
`42`	None; the supplied value is an instance of `xs:integer`, which is a subtype of the required type.
`math:pi()`	The supplied value is an instance of `xs:double`, which can be converted to `xs:decimal` under the coercion rules.
`("a", "b")[.="c"]`	The supplied value is an empty sequence, which is a valid instance of the required type `xs:decimal?`. However, the processor may (optionally) reject this as an implausible coercion, on the grounds that it can only succeed in one special case, namely where the filter expression selects no values.
`(1.5, 2.5, 3.5)`	A type error is raised, except in the case where XPath 1.0 compatibility is enabled, in which case all values after the first are discarded.
`<a>3.14159</a>`	The element node is atomized; unless it has been schema-validated, the result will be `"3.14159"` as an instance of `xs:untypedAtomic`. This is converted to an instance of `xs:decimal` following the rules of the `cast as` operator.
`"12.2"`	Supplying a string where an `xs:decimal` is a type error, even if XPath 1.0 compatibility mode is enabled. The rules for compatibility mode would allow conversion if the required type were `xs:double`, but not for `xs:decimal`.
`[1.5]`	The array is atomized, and the result is a valid instance of the required type `xs:decimal?`
`[]`	The array is atomized, and the result is an empty sequence, which is a valid instance of the required type `xs:decimal?`
Supplied Value	Coercion
`12`	The supplied value is of type `xs:integer`. Because the supplied value and the required type, `xs:positiveInteger`, both come under the primitive type `xs:decimal`, and the value `12` is within the value space of `xs:positiveInteger`, the value is relabeled as an `xs:positiveInteger` and the call succeeds.
`12.1`	This fails with a type error, because the `xs:decimal` value `12.1` is not a value in the value space of `xs:positiveInteger`. This is so even though casting to `xs:positiveInteger` would succeed.
`math:pi()`	This fails with a type error. A value of type `xs:double` is accepted where the required type is `xs:decimal` or `xs:float`, but not where it is `xs:positiveInteger`.
`<a>1200</a>`	The supplied element node is atomized. If the element has not been schema-validated, the result will be an `xs:untypedAtomic` item, which is successfully cast to the required type `xs:positiveInteger`. If the element has been validated against a schema, then coercion succeeds if the typed value would itself be acceptable, for example if it is an `xs:positiveInteger`, or some other `xs:decimal` within the value space of `xs:positiveInteger`.
Supplied Value	Coercion
`"amp"`	The supplied value is of type `xs:string`, which is one of the allowed types. The call therefore succeeds.
`"#"`	The supplied value is of type `xs:string`, which is one of the allowed types. As far as the coercion rules are concerned, the call therefore succeeds. Under the semantic rules for the `fn:char` function, however, this value is not accepted; a dynamic error (as distinct from a type error) is therefore raised.
`0x25`	The supplied value is of type `xs:integer`. Although this is not one of the allowed types, it is acceptable because coercion of the value to type `xs:positiveInteger` succeeds. The value is relabeled as an instance of `xs:positiveInteger`.
`<a>0x25</a>`	The supplied element node is atomized. Assuming that the node has not been schema-validated, the result is an instance of `xs:untypedAtomic`. The member types of the choice are tested in order. Conversion to `xs:string` with the value "0x25" succeeds, so the `fn:char` function is called supplying this string; but the function rejects this string as semantically invalid. The same would happen if the value were, say, <a>37</a>. Supplying such a value requires an explicit cast, for example `fn:char( xs:positiveInteger( ./a ))`.
Supplied Value	Coercion
`{ "x": 1, "y": 2, "z": 3 }`	The supplied value is an instance of the first record type: no coercion is necessary.
`{ "size": "M" }`	The supplied value is an instance of the second record type: no coercion is necessary.
`{ "x": 1, "y": 2, "size": "XL" }`	The supplied value is an instance of both record types: no coercion is necessary.
`{ "x": 1e0, "y": 2e0, "size": "XL" }`	The supplied value is not an instance of the first record type because the fields are of type `xs:double` rather than `xs:decimal`. It is however an instance of the second record type. It is therefore accepted as is; the fields `x` and `y` are not converted from `xs:double` to `xs:decimal`.
`{ "x": 1e0, "y": 2e0, "size": "XXL" }`	The supplied value is not an instance of the first record type because the fields are of type `xs:double` rather than `xs:decimal`, and it is not an instance of the second record type because the `size` value does not match the enumeration type. Coercion is therefore attempted to the first record type, and succeeds. The `x` and `y` fields are coerced to `xs:decimal`, and the `size` field is accepted as is.
[1]	`XPath`	::=	`Expr`
`Expr`
[46]	`Expr`	::=	`(ExprSingle ++ ",")`
`(ExprSingle ++ ",")`
[47]	`ExprSingle`	::=	`ForExpr \| LetExpr \| FLWORExpr \| QuantifiedExpr \| SwitchExpr \| TypeswitchExpr \| IfExpr \| TryCatchExpr \| OrExprPipelineExpr`
`ForExpr \| LetExpr \| FLWORExpr \| QuantifiedExpr \| SwitchExpr \| TypeswitchExpr \| IfExpr \| TryCatchExpr \| OrExprPipelineExpr`
[282283]	`Comment`	::=	`"(:" (CommentContents \| Comment)* ":)"`	/* ws: explicit */
`"(:" (CommentContents \| Comment)* ":)"`	/* ws: explicit */
		/* ws: explicit */
		/* gn: comments */
[295296]	`CommentContents`	::=	`(Char+ - (Char* ('(:' \| ':)') Char*))`	/* ws: explicit */
`(Char+ - (Char* ('(:' \| ':)') Char*))`	/* ws: explicit */
		/* ws: explicit */
[170171]	`PrimaryExpr`	::=	`Literal \| VarRef \| ParenthesizedExpr \| ContextValueRef \| FunctionCall \| OrderedExpr \| UnorderedExpr \| NodeConstructor \| FunctionItemExpr \| MapConstructor \| ArrayConstructor \| StringTemplate \| StringConstructor \| UnaryLookup`
`Literal \| VarRef \| ParenthesizedExpr \| ContextValueRef \| FunctionCall \| OrderedExpr \| UnorderedExpr \| NodeConstructor \| FunctionItemExpr \| MapConstructor \| ArrayConstructor \| StringTemplate \| StringConstructor \| UnaryLookup`
[209210]	`FunctionItemExpr`	::=	`NamedFunctionRef \| InlineFunctionExpr`
`NamedFunctionRef \| InlineFunctionExpr`
[171172]	`Literal`	::=	`NumericLiteral \| StringLiteral`
`NumericLiteral \| StringLiteral`
[172173]	`NumericLiteral`	::=	`IntegerLiteral \| HexIntegerLiteral \| BinaryIntegerLiteral \| DecimalLiteral \| DoubleLiteral`
`IntegerLiteral \| HexIntegerLiteral \| BinaryIntegerLiteral \| DecimalLiteral \| DoubleLiteral`
[266267]	`IntegerLiteral`	::=	`Digits`	/* ws: explicit */
`Digits`	/* ws: explicit */
		/* ws: explicit */
[267268]	`HexIntegerLiteral`	::=	`"0x" HexDigits`	/* ws: explicit */
`"0x" HexDigits`	/* ws: explicit */
		/* ws: explicit */
[268269]	`BinaryIntegerLiteral`	::=	`"0b" BinaryDigits`	/* ws: explicit */
`"0b" BinaryDigits`	/* ws: explicit */
		/* ws: explicit */
[269270]	`DecimalLiteral`	::=	`("." Digits) \| (Digits "." Digits?)`	/* ws: explicit */
`("." Digits) \| (Digits "." Digits?)`	/* ws: explicit */
		/* ws: explicit */
[270271]	`DoubleLiteral`	::=	`(("." Digits) \| (Digits ("." Digits?)?)) [eE] [+-]? Digits`	/* ws: explicit */
`(("." Digits) \| (Digits ("." Digits?)?)) [eE] [+-]? Digits`	/* ws: explicit */
		/* ws: explicit */
[289290]	`Digits`	::=	`DecDigit ((DecDigit \| "_")* DecDigit)?`	/* ws: explicit */
`DecDigit ((DecDigit \| "_")* DecDigit)?`	/* ws: explicit */
		/* ws: explicit */
[290291]	`DecDigit`	::=	`[0-9]`	/* ws: explicit */
`[0-9]`	/* ws: explicit */
		/* ws: explicit */
[291292]	`HexDigits`	::=	`HexDigit ((HexDigit \| "_")* HexDigit)?`	/* ws: explicit */
`HexDigit ((HexDigit \| "_")* HexDigit)?`	/* ws: explicit */
		/* ws: explicit */
[292293]	`HexDigit`	::=	`[0-9a-fA-F]`	/* ws: explicit */
`[0-9a-fA-F]`	/* ws: explicit */
		/* ws: explicit */
[293294]	`BinaryDigits`	::=	`BinaryDigit ((BinaryDigit \| "_")* BinaryDigit)?`	/* ws: explicit */
`BinaryDigit ((BinaryDigit \| "_")* BinaryDigit)?`	/* ws: explicit */
		/* ws: explicit */
[294295]	`BinaryDigit`	::=	`[01]`	/* ws: explicit */
`[01]`	/* ws: explicit */
		/* ws: explicit */