The differences function (comparing two xml files) is very rare in the Eclipse plugin ecosystem (and, of course, not in the WTP environment ).
I only know about a commercial tool like XML Diff & Merge , which offers the following : <oXygen/>

(source: oxygenxml.com )
diff XML diff (XML Accurate - XML Fast - ), , , <oXygen/> XML Diff , : , . , <oXygen/> XML Diff , .
XML diff , , XML. , , , , , , , CDATA, DOCTYPE, .
