867 Add an explanation of default value expressions in function signa…

…tures.

specifications/xpath-functions-40/src/xpath-functions.xml

@@ -555,7 +555,14 @@ for transition to Proposed Recommendation. </p>'>
                as a keyword in a function call)</p></item>
                <item><p>The static type of the parameter (in italics)</p></item>
                <item><p>If the parameter is optional, then an expression giving the default value 
-                  (preceded by the symbol <code>:=</code>).</p></item>
+                  (preceded by the symbol <code>:=</code>).</p>
+                     <p diff="add" at="2023-12-04">The default value expression is evaluated using the static and
+                     dynamic context of the function caller (or of a named function reference). For example, 
+                     if the default value is given as <code>.</code>, then it evaluates to the context value 
+                     from the dynamic context of the function caller; if it is given as <code>default-collation</code>,
+                     then its value is the default collation from the static context of the function caller;
+                     if it is given as <code>deep-equal#2</code>, then the third argument supplied to <code>deep-equal</code>
+                     is the default collation from the static context of the caller.</p></item>
             </ulist>
             <p>If there are two or more parameter declarations, they are separated by a comma.</p> 
             <p>The <emph> <code>return-type</code></emph>, also in italics, specifies the static type of the value returned by the