[xslt] Use an external program for some tags

[Daniel Bonniot <Daniel Bonniot inria fr>]

Hi,

I have a docbook document that i'd like to transform. It includes 
'programlisting' elements, on which I would like to apply 
syntax-highlighting. I happen to have a binary program (highlight) that 
can process the program text into fo format. So what I would like is to 
make xsltproc apply a stylesheet to produce fo for my docbook file, but 
call the highlight program on programlisting elements, and include its 
output. Is there a way to do this cleanly? I would imagine a 
xsl:template rule that would instruct to call an external program, but 
could not find a function to do that. I understand this might sound a 
bit alien in the XSLT world, but it would be very handy in some situations.

Thanks for your help,

Daniel