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Allow composite sort keys in xsl:sort
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@michaelhkay
michaelhkay committed Jan 3, 2025
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Showing 1 changed file with 60 additions and 30 deletions.
90 changes: 60 additions & 30 deletions specifications/xslt-40/src/xslt.xml
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Expand Up @@ -22940,6 +22940,15 @@ return if ($i le count($S))
</div3>
<div3 id="comparing-sort-keys">
<head>Comparing Sort Key Values</head>
<changes>
<change>
Numeric values of type <code>xs:decimal</code> are compared
as decimals, without first converting to <code>xs:double</code>.
</change>
<change issue="1662">
Composite sort keys are allowed in <elcode>xsl:sort</elcode>.
</change>
</changes>
<p>It is possible to force the system to compare <termref def="dt-sort-key-value">sort key values</termref> using the rules for a particular datatype by
including a cast as part of the <termref def="dt-sort-key-component">sort key
component</termref>. For example, <code>&lt;xsl:sort
Expand All @@ -22966,30 +22975,64 @@ return if ($i le count($S))
the <elcode>xsl:sort</elcode> element has a value other than <code>text</code> or
<code>number</code>, the effect is implementation-defined.</imp-def-feature>
<p>
<error spec="XT" type="type" class="TE" code="1020">
<p>If any <termref def="dt-sort-key-value">sort key value</termref>, after
If the <elcode>xsl:sort</elcode> element is processed with <termref def="dt-xslt-10-behavior">XSLT 1.0
behavior</termref>,
then if any <termref def="dt-sort-key-value">sort key value</termref>, after
<termref def="dt-atomization">atomization</termref> and any type
conversion <rfc2119>required</rfc2119> by the <code>data-type</code>
attribute, is a sequence containing more than one item, then the effect
depends on whether the <elcode>xsl:sort</elcode> element is processed with <termref def="dt-xslt-10-behavior">XSLT 1.0
behavior</termref>. With XSLT 1.0 behavior, the effective
sort key value is the first item in the sequence. In other cases, this is a
<termref def="dt-type-error">type error</termref>.</p>
</error>
</p>
<p>The set of <termref def="dt-sort-key-value">sort key values</termref> (after any
conversion) is first divided into two categories: empty values, and ordinary
values. The empty sort key values represent those items where the sort key value
is an empty sequence. These values are considered for sorting purposes to be equal
to each other, but less than any other value. The remaining values are classified
as ordinary values.</p>
attribute, is a sequence containing more than one item, then the effective
sort key value is the first item in the sequence.</p>

<p>In general the <termref def="dt-sort-key-value">sort key values</termref> (after any
conversion) are sequences of atomic items. Two sequences of atomic items
<var>S1</var> and <var>S2</var> are compared as follows:</p>

<olist>
<item><p>If both <var>S1</var> and <var>S2</var> are empty sequences,
then they compare equal.</p></item>
<item><p>A sequence that is empty is considered to be less than
a sequence that is not empty.</p></item>
<item><p>If neither sequence is empty, then
<code>head(<var>S1</var>)</code> and
<code>head(<var>S2</var>)</code> are compared
according to the rules below.</p>
<olist>
<item><p>If they compare equal, the result is obtained
by comparing <code>tail(<var>S1</var>)</code> to
<code>tail(<var>S2</var>)</code>.</p></item>
<item><p>Otherwise, the result of comparing these two
items is used as the result of the sequence comparison.</p></item>
</olist></item>
</olist>
<p>For example:</p>
<ulist>
<item><p><code>(1, 2, 3)</code> precedes <code>(1, 2, 4)</code>.</p></item>
<item><p><code>(1, 2)</code> precedes <code>(1, 2, 3)</code></p></item>
<item><p><code>()</code> precedes <code>(1, 2)</code></p></item>
</ulist>
<p diff="chg" at="2023-12-06">Individual atomic items are compared as follows:</p>
<olist diff="chg" at="2023-12-06">
<item><p>If both values are instances of <code>xs:string</code>, <code>xs:anyURI</code>,
or <code>xs:untypedAtomic</code>, they are compared using the appropriate collation,
as described in the next section.</p></item>
<item><p>If both values are instances of <code>xs:numeric</code>, they are compared
using the <xfunction>compare</xfunction> function.</p>
<note><p>This is a change from earlier versions, since <code>xs:decimal</code> values are now compared
as decimals, rather than being first converted to <code>xs:double</code>.</p></note></item>
<item><p>In all other cases, values are compared according to the rules
of the XPath <code>lt</code> operator. This will raise an error if the values are
not comparable (for example, if one is an <code>xs:integer</code> and the other is
an <code>xs:date</code>).</p></item>
</olist>


<p>
<error spec="XT" type="dynamic" class="DE" code="1030">
<p>It is a <termref def="dt-dynamic-error"> dynamic error</termref> if, for any <termref def="dt-sort-key-component">sort key component</termref>, the set of
<termref def="dt-sort-key-value">sort key values</termref> evaluated for
all the items in the <termref def="dt-initial-sequence">initial
sequence</termref>, after any type conversion requested, contains a pair
of ordinary values for which the result of the XPath <code>lt</code>
of atomic items for which the result of the XPath <code>lt</code>
operator is an error. If the processor is
able to detect the error statically, it <rfc2119>may</rfc2119> optionally
raise it as a <termref def="dt-static-error">static
Expand All @@ -23009,20 +23052,7 @@ return if ($i le count($S))
the corresponding major sort key values are equal.</p>
</note>

<p diff="chg" at="2023-12-06">Individual values are compared as follows:</p>
<olist diff="chg" at="2023-12-06">
<item><p>If both values are instances of <code>xs:string</code>, <code>xs:anyURI</code>,
or <code>xs:untypedAtomic</code>, they are compared using the appropriate collation,
as described in the next section.</p></item>
<item><p>If both values are instances of <code>xs:numeric</code>, they are compared
using the <xfunction>compare</xfunction> function.</p>
<note><p>This is a change from earlier versions, since <code>xs:decimal</code> values are now compared
as decimals, rather than being first converted to <code>xs:double</code>.</p></note></item>
<item><p>In all other cases, values are compared according to the rules
of the XPath <code>lt</code> operator. This will raise an error if the values are
not comparable (for example, if one is an <code>xs:integer</code> and the other is
an <code>xs:date</code>).</p></item>
</olist>


</div3>
<div3 id="collating-sequences">
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