I'm doing it like this:

  <xsl:variable name="level" select="count(ancestor::Menu)"/>
  (...)
  <xsl:choose>
	<xsl:when test="$level=0">
		<xsl:text>1</xsl:text>   ----> this node is visible
	</xsl:when>

  where Menu is your tree_node.



that (probably) forces the system to really go all the way up the
ancestor axis and count the number of nodes.

If you just went
 
<xsl:when test="not(ancestor::Menu)">1</xsl:when>


then the system would only need to do the minimum amount of checking to
see if there were any such ancestors.

David

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