Re: B.2 DTD required or optional?

I like Tim Bray's distinction of well-formed and valid. The concepts are easily understood and have practical (not just theoretical) 

In my opinion, it must be possible to correctly process well-formed XML without 
the aid of a DTD. Ideally, well-formed documents would be processed without any 
form of "hinting". If we cross the DTD-less line for well-formed XML, I doubt 
that XML will be widely accepted.