Norm Walsh has published
DocBook NG: The “Jägermeister” Release; a.k.a. beta 10 of DocBook 5.0.
DocBook NG is
"a significant redesign that attempts to remain true to the spirit of DocBook."
The schema is written in
RELAX NG. A DTD generated from the RELAX NG schema is also available.
Jägermeister adds mathphrase and termdef elements.