Affects Version/s: DocBook 5.1
Fix Version/s: None
Component/s: Public reviews
1.2 Normative References reads in part:
[DocBook 5: TDG] Norman Walsh. DocBook 5.0: The Definitive Guide. O'Reilly Media. April 2010.
Aside from the question of citing non-normative material as normative, this reference isn't used in the draft.
The one possible reference, under Appendix A 1:
This media type registration is for DocBook documents as described by [DocBook 5: TDG].
In fact has a URL that points to Docbook 5.1.
That being the case, the reference with the label DocBook 5 can be dropped.