> I'd like to track changes between two documents (e.g. between
> two versions of a paragraph, current and last) and sign that changes
> with, I don't know, different colors.
"Changes between documents" is a difficult issue where XML is concerned
because of the difficulty of distinguishing between merely lexical changes
and those that affect the infoset. Even assuming you are content to detect
and record the latter, things can get very tricky if your documents have
complex structures. eXist currently has no support for this sort of thing,
but anything that can be coded in Java can be added as an XQuery extension.
I imagine the best place to start might be to take a good look at
http://www.alphaworks.ibm.com/tech/xmldiffmerge/ and take things from there...
You also might want to check out how oXygen (http://www.oxygenxml.com)
does it. They have a pretty good program that sounds like it does
exactly what you're looking for, and it can pull files in over http, so
it should be a simple matter to get it to work with eXist.