> the Unicode characters to which Joe was referring to are
 > those appearing in element tag names, rather than DTD
 > elemment declarations.

No, I was referring to both.

> Wouldn't you just use a character entity?

You could. But you don't need to, and generally you wouldn't if you were 
working in an encoding which supported that character. That's the whole 
point of being able to specify the encoding, after all -- to be able to 
enter characters directly rather than via awkward workarounds.

Of course Unicode covers *all* those characters (well, all those in any 
natural language plus some symbols plus -- unofficially -- some 
artificial languages like Klingon) and can express them directly. Which 
is why the default encoding, if you don't specify otherwise, is assumed 
to be one of the Unicode encodings (UTF-8 or UTF-16).

Your processor, if you're still determined to write one, doesn't have to 
support all possible encodings -- but it really should support UTF-8 and 
UTF-16 if you want to claim you correctly implement the XML 
Recommendation. If you're working in Java, that's relatively easy; Java 
defaults to UTF-8 files and UTF-16 internally. In other languages it may 
take more work, and/or tracking down support libraries.

That's a good example of the kind of nickpicky detail that makes 
implementing a complete XML parser/serializer less than completely 
trivial. Still want to write your own?