<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
>

<xsl:key name="kComDesc" match="h1|p|b|i"
  use="exists(ancestor::Comments[1])"/>

<xsl:template match="key('kComDesc', 'true')">
  Whatever processing here
</xsl:template>
</xsl:stylesheet>

--
Cheers,
Dimitre Novatchev
---------------------------------------
Truly great madness cannot be achieved without significant intelligence.
---------------------------------------
To invent, you need a good imagination and a pile of junk
-------------------------------------
You've achieved success in your field when you don't know whether what
you're doing is work or play

> But it's free enough to support a bit of a workaround, even
> if you have no schema:
>
> <xsl:variable name="comment-elements"
> select="//comments//(h1|p|b|i)"/>
>
> <xsl:template match="*[exists(. intersect $comment-elements)]">
>     ...
> </xsl:template>
>
> I think this should work.

Yes, but it might have fairly horrible performance.

I don't know how other processors work, but with Saxon, patterns are a lot
more efficient if they identify the element names that match, because Saxon
basically does a hash lookup on the node kind and then on the node name. Any
match="*" pattern gets tested against every node; and in this case that will
involve a serial search through the list of h1|p|b|i elements, which is
distinctly O(n^2). Not worth the savings in keystrokes.

Michael Kay
http://www.saxonica.com/