> What is the best way to find out whether a variable is a string or a
> tree ?


You can't. Well for a variable you can as you just need to look at the
text of the stylesheet, it never depends on run time behaviour, but for
a parameter it is not possible to tell without using an extension
function.

<xsl:variable name="treeTest">
 <node> 
    <xsl:copy-of select="$cmdRequest"/>
 </node>
</xsl:variable> 
<xsl:choose>
  <xsl:when test="$treeTest/node/node()">

                           ^ that is a syntax error, you can not (in
                           XSLT 1) apply / to result tree fragment
                           variables.

David

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