calling function with xslt using xpath selection

Here is an example from the MSXML 4 SDK (this should be the same for MSXML 6, and is quite similar for .NEt's XslCompiledTransform -- for the latter search MSDN for <msxsl:script>)

Example This example defines a script block with a namespace prefix of user that contains a function called xml that takes a node-list as an argument. Later, this function, xml(nodelist) in the user namespace, is called from the select attribute of .

XML File (customers.xml)

<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="script.xsl" ?>
<customers>
   <customer>
      <name>John Smith</name>
      <address>123 Elm St.</address>
      <phone>(123) 456-7890</phone>
   </customer>
   <customer>
      <name>Mary Jones</name>
      <address>456 Oak Ave.</address>
      <phone>(156) 789-0123</phone>
   </customer>
</customers>

XSLT File (script.xsl)

<?xml version='1.0'?>
<xsl:stylesheet version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
      xmlns:msxsl="urn:schemas-microsoft-com:xslt"
      xmlns:user="http://mycompany.com/mynamespace">

<msxsl:script language="JScript" implements-prefix="user">
   function xml(nodelist) {
      return nodelist.nextNode().xml;
   }
</msxsl:script>

<xsl:template match="/">
   <xsl:value-of select="user:xml(.)"/>
</xsl:template>

</xsl:stylesheet>

Formatted Output

<?xml version="1.0" encoding="UTF-16"?>&lt;?xml version="1.0"?&gt;
&lt;?xml-stylesheet type="text/xsl" href="script.xsl" ?&gt;
&lt;customers&gt;
 &lt;customer&gt;
  &lt;name&gt;John Smith&lt;/name&gt;
  &lt;address&gt;123 Elm St.&lt;/address&gt;
  &lt;phone&gt;(123) 456-7890&lt;/phone&gt;
 &lt;/customer&gt;
 &lt;customer&gt;
  &lt;name&gt;Mary Jones&lt;/name&gt;
  &lt;address&gt;456 Oak Ave.&lt;/address&gt;
  &lt;phone&gt;(156) 789-0123&lt;/phone&gt;
 &lt;/customer&gt;
&lt;/customers&gt;