<xsl:stylesheet version="1.0" 
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xalan="http://xml.apache.org/xslt"
xmlns:trig="http://www.acmeX.com/extend/trig">
  
<xalan:component prefix="trig" functions="sin cons tan atan">
  <xalan:script lang="javascript">
    function sin (arg){ return Math.sin(arg);} 
    function cos (arg){ return Math.cos(arg);} 
    function tan (arg){ return Math.tan(arg);} 
    function atan (arg){ return Math.atan(arg);} 
  </xalan:script>
</xalan:component>
   
<xsl:variable name="PI" select="4.0 * trig:atan(1.0)"/>
   
<!-- ... -->
   
</xsl:stylesheet>

Saxon currently supports JavaScript, NetRexx, BML, JPython, Jacl, JScript, VBScript, and PerlScript, but appropriate extensions need to be obtained from third parties supporting the respective languages. See http://xml.apache.org/xalan-j/extensions.html#supported-lang for details.