defining xml diff/changes in xml : XUpdate etc

Hi,

Im looking for a standard for defining xml diffs/changes in an xml format 
(which may be used for patching later).
I've looked at Xupdate, and its quite close to what im looking for.
http://xmldb-org.sourceforge.net/xupdate/xupdate-wd.html

however, im concerned if this is a "standard", or is widely popular.
What makes me queasy is that their domain site http://www.xmldb.org, is no 
longer theirs (or doesnt seem to be).

If anyone has experience with xml diffs and can point me to a relatively 
stable standard, your help is appreciated.
The icing would be a OSS api that diffs xmls and generates this standard.

thanks,

regards,
rax