That'll hurt efforts to make content transitions seamless using content 
negotiation, though.  Not that having ten steps between 2.0 and 3.0 
isn't, I suppose.  Although, I agree that forcing serialization could be 
asking for trouble - if say a browser implemented maths and not tables, 
and maths were HTML 2.2 and tables 2.1, then the browser couldn't claim 
to accept "HTML 2.2", etc.
What we *could* do is give each incremental advance its own temporary 
mime type, like text/x-html-tables, text/x-html-maths, etc.  For 
documents in which we want to use both tables and maths, we use <A 
REL="include"> or some such to include the text/x-html-maths in a 
text/html document, at least until we have something we can call 
text/html; level=3.
	Brian
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