The latter is the case I was thinking of. Purportedly xml-stylesheet 
  supports this, but I've never seen it work in a browser. (I'd be grateful 
  if anyone can show me how.)

http://www.bayes.co.uk/xml/portal.aspx?page=/xml/index.xml&subpage=/xml/utils/multiple.xml

________________________________________________________________________
This e-mail has been scanned for all viruses by Star. The
service is powered by MessageLabs. For more information on a proactive
anti-virus service working around the clock, around the globe, visit:
http://www.star.net.uk
________________________________________________________________________