[xsl] Capturing result of <xsl:apply-templates/> in a variable

[David Sewell <dsewell@xxxxxxxxxxxx>]

Just now when writing a transform, for temporary diagnostic purposes I 
needed to produce messages showing (1) the initial string value of an 
input element before template application, and (2) the output string value 
after template application. Oddly enough I have never before wanted to 
do precisely that task.

A moment's reflection suggested that I could capture the result of 
<xsl:apply-templates/> and use it as a variable, thus (given XSLT 2.0):

<xsl:template match="INPUT">
  <xsl:variable name="appliedTemplates" as="item()+">
    <xsl:apply-templates/>
  </xsl:variable>
  <OUTPUT>
    <xsl:copy-of select="$appliedTemplates"/>
  </OUTPUT>
  <xsl:message>Old value: <xsl:value-of select="."/></xsl:message>
  <xsl:message>New value: <xsl:value-of select="$appliedTemplates"/></xsl:message>
</xsl:template>

This was probably the first time in my years of working with XSLT that 
it occurred to me to capture <xsl:apply-templates/> in a variable (I'll 
never be an XSLT wizard). I'm wondering: is the procedure above 
guaranteed to work in all cases, or is it possible that the 
<xsl:copy-of select="$appliedTemplates"/> could ever return something 
different from <xsl:apply-templates/> in this context? And is this the best 
strategy for comparing input and output states of a template (assuming string 
value is the only concern)?

David S.

--
David Sewell, Editorial and Technical Manager
ROTUNDA, The University of Virginia Press
PO Box 400314, Charlottesville, VA 22904-4314 USA
Email: dsewell@xxxxxxxxxxxx   Tel: +1 434 924 9973
Web: http://rotunda.upress.virginia.edu/