Function use in a pre-2.0 stylesheet

xsl:function was introduced in XSLT 2.0. A stylesheet that declares version="1.0" (or 1.1) but defines an xsl:function cannot run on a 1.0 processor — the instruction does not exist there. What decides it is the version in force over the function, which is the nearest one declared above it rather than the root's: XSLT lets version sit on any of its own elements and xsl:version on any literal result element, each setting the version of everything beneath. So a 1.1 stylesheet is caught as plainly as an explicit 1.0, and one declaring no version at all names no processor to be wrong about — a missing version is its own fault, reported as itself.

Either replace the function with an xsl:template that has a name, or raise the stylesheet to version="2.0".

Incorrect:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <xsl:function name="my:foo">
    <!-- body logic -->
  </xsl:function>
</xsl:stylesheet>

Correct:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <xsl:template name="foo">
    <!-- body logic -->
  </xsl:template>
</xsl:stylesheet>

or:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="2.0">
  <xsl:function name="my:foo">
    <!-- body logic -->
  </xsl:function>
</xsl:stylesheet>