Need help finding invalid references to target IDs

Hi,

This is probably a newbie question, although I've hacked a lot of XSLT
for about a year.  This problem has me stumped, however.

Our schema has numerous elements with "id" attributes (target IDs) and
several with "refID" attributes (reference IDs).  Unfortunately, these
are not defined as ID and IDREF respectively or I wouldn't be having
this issue.  I need to compare all of the "refID" attributes in a
document against all of the "id" attributes and generate a report
showing the "refID" attributes that do not have a valid target.  I know
this is probably only a few lines in XSLT, but I'm not sure where to
even start to do this test.

Can anyone get me started?

Dave Hintz