Thanks Michael for responding my question so quickly.

The unsupported.xml could have following XML structure:

<unsupported>
   <!--... ALL UNSUPPORTED NODES LISTED HERE ...-->
   <node name="name_of_unsupported_node"
xpath="xpath_to_unsupported_node"/>
</unsupported>

The main idea here is, that when the application reads the upgraded
4.x configuration and it shows an information dialog were it
displays those unsupported 3.x XML elements.

<xsl:result-document href="unsupported.xml">
  <unsupported>
    <xsl:for-each select="//all_unsupported_nodes">
      ...
    </xsl:for-each>
  </unsupported>
</xsl:result-document>

Michael Kay's answer tells me it is not that easy and you may need a
two-step process:

1) mark all unsupported nodes and process all supported nodes as
desired using Michael example:

<xsl:template match="*">
  <xxx:untransformed-element>
    <xsl:copy-of select="."/>
    (or perhaps <xsl:apply-templates/>)
  </xxx:untransformed-element>
</xsl:template>

2) take this intermediate XML and filter all marked nodes to
unsupported.xml

<xsl:template match="/">
  <!-- create a file with the unsupported nodes -->
  <xsl:result-document href="unsupported.xml">
    <unsupported>
      <xsl:for-each select="//xxx:untransformed-element">
        <xsl:copy-of select="."/>
      </xsl:for-each>
    </unsupported>
  </xsl:result-document>
  <!-- pass through all but the above elements -->
  <xsl:apply-templates select="node()[name()!='xxx:untransformed-
element']" />
</xsl:template>

<!-- identity transform does the rest -->
<xsl:template match="element()">
  <xsl:copy>
    <xsl:apply-templates select="@*,node()"/>
   </xsl:copy>
</xsl:template>

<xsl:template match="attribute()|text()|comment()|processing-
instruction()">
  <xsl:copy/>
</xsl:template>

By the way, what do you mean with "identity transform template"?

See <http://ajwelch.blogspot.com/2008/01/indentity-transform-for-
xslt-20.html> and the XSLT FAQ by Dave Pawson.

--
_______________________________________________________________
Michael M|ller-Hillebrand: Dokumentations-Technologie
Adobe Certified Expert, FrameMaker
Lvsungen und Training, FrameScript, XML/XSL, Unicode
<http://cap-studio.de/> -- Tel. +49 (9131) 28747