The HTML WG did it again. The XHTML™ Modularization 1.1 document introduces several controversial changes while moving from the second working draft to W3C Proposed Recommendation, skipping the quite important Last Call and W3C Candidate Recommendation phases. There is a diff-marked version. According to this draft any element can have an xhtml:onkeypress attribute, or xhtml:style. While you might think xml:id is enough the WG brings you xhtml:id (when xhtml is bound to the right namespace). Reading the draft it seems this was not a simple editorial mistake.
In process, they managed not to fix known outstanding issues and although the 1.1 version is now “newer” XHTML 1.0 is still better.
Anyway, if there is one thing you should read today it is Björn Höhrmann’s excellent e-mail titled The xhtml:onkeypress architecture. Spot on!