> Is there anything I can do except generating the
> stylesheet on the fly ?

It depends on how general you want to be.

If you have a finite list of possible sensible values for the query
parameter, you can have an xsl:choose that just does a different
call to apply templates depending on the value of $query.

If query can be arbitrary, but is only ever an element name not a full
xpath expression (and you are not too namespace aware) you can go

 <xsl:apply-templates select="*[name(.)=$query]"/>

Anything other than those two cases, I think you probably do want to
generate the stylesheet from the query string.

David


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