Extensibility and Versioning in SMIL 2.0 (and 1.0)

I'm still digesting "Versioning XML Languages
Proposed TAG Finding 16 November 2003"

http://www.w3.org/2001/tag/doc/versioning.html

I wanted to point out that the issue of language versioning has been 
addressed in SMIL 2.0 -

Various relevant links include
http://www.w3.org/TR/smil20/smil20-profile.html#SMILProfileNS-Extending
http://www.w3.org/TR/smil20/smil-content.html#ContentControlNS-SkipContent
http://www.w3.org/TR/smil20/smil20-profile.html#SMILProfileNS-AgentConformance
http://www.w3.org/TR/smil20/smil-basic.html#BaseGuideNS-BasicUserAgent

(an extension mechanism has also been in SMIL 1.0, but that is probably 
subsumed by the above)

This is mostly an FYI (in case this was missed - maybe there are new 
aspects in the design above - it took quite some time to design, as far 
as I remember). It would probably also be interesting to have comments 
on how SMIL would fit into the versioning framework built by the TAG.

-Philipp