[xsl] surprised about the results of a filter expression in XSLT2.0

[alan.painter@xxxxxxxxx]

I'm surprised to see that a filter expression, applied in this case to a
variable, produces more elements in the result than there are elements in
the variable.  In this case, it produces the cartesian product of the
number of elements in the variable and the number of combinations in the
list that comprises the predicate.  I'm assuming that this is normal.
Where can I find this behavio(u)r described in the XSLT spec?  Thanks for
any pointers.

In Saxon 8.7.1 (perhaps elsewhere but haven't tested), in the below
stylesheet, the instruction

      <xsl:copy-of select="$idElements[@id=$hrefs]"/>

produces

   <idElement id="_123"/>
   <idElement id="_123"/>
   <idElement id="_123"/>
   <idElement id="_456"/>
   <idElement id="_456"/>
   <idElement id="_456"/>

whereas the instruction

      <xsl:copy-of select="$idElements[@id=distinct-values($hrefs)]"/>

produces

   <idElement id="_123"/>
   <idElement id="_456"/>

Here's the stylesheet

<?xml version="1.0" encoding="UTF-8"?>

<xsl:stylesheet xmlns:xs="http://www.w3.org/2001/XMLSchema";
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
                xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
                version="2.0">

      <xsl:output method="xml" encoding="ISO-8859-1" indent="yes"/>

      <xsl:variable name="testdoc">
            <root>
                  <refElement name="element1"> <ref href="_123"/>
</refElement>
                  <refElement name="element2"> <ref href="_123"/>
</refElement>
                  <refElement name="element3"> <ref href="_123"/>
</refElement>
                  <refElement name="element4"> <ref href="_456"/>
</refElement>
                  <refElement name="element5"> <ref href="_456"/>
</refElement>
                  <refElement name="element6"> <ref href="_456"/>
</refElement>
                  <idElement id="_123"/>
                  <idElement id="_456"/>
                  <idElement id="_789"/>
            </root>
      </xsl:variable>

      <xsl:variable name="idElements" select="$testdoc//idElement"/>

      <xsl:template match="/">
            <xsl:apply-templates select="$testdoc" mode="inTestDoc"/>
      </xsl:template>

      <xsl:template match="*" mode="inTestDoc">
            <xsl:variable name="hrefs" as="xs:string*"
select="$testdoc//@href"/>
            <xsl:copy>
                  <!-- Case 1 -->
                  <xsl:copy-of select="$idElements[@id=$hrefs]"/>
                  <!-- Case 2 -->
                  <!-- <xsl:copy-of
select="$idElements[@id=distinct-values($hrefs)]"/> -->
            </xsl:copy>
      </xsl:template>

</xsl:stylesheet>

Output of case 1:

<?xml version="1.0" encoding="ISO-8859-1"?>
<root xmlns:xs="http://www.w3.org/2001/XMLSchema";
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";>
   <idElement id="_123"/>
   <idElement id="_123"/>
   <idElement id="_123"/>
   <idElement id="_456"/>
   <idElement id="_456"/>
   <idElement id="_456"/>
</root>

Output of case 2:

<?xml version="1.0" encoding="ISO-8859-1"?>
<root xmlns:xs="http://www.w3.org/2001/XMLSchema";
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";>
   <idElement id="_123"/>
   <idElement id="_456"/>
</root>

-alan
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