DOCBOOK: DocBook 5.0, 6.0 etc.

Since a couple of versions ago, the information on furture changes in the
DocBook DTD have been removed from appendix C in the TDG. Is there any
reason for this. I liked knowing in advance, what elements would be
removed, added etc. 

With that info, I was able to reasonable sure, my documents are valid in
furture releases of the DTD.

Regards

Jens