Case usage in element names, attribute names & attribute val

I've been looking through many of the established XML grammars, and am
left with a question.  Why do all the grammars appear to be in
lower-case?  Since xml has become case-sensitive, it would seem to me
that people would adopt one of the popular conventions used in other
case-sensitive applications like programming languages.  Why haven't I
seen any grammars that look like this:

<TagName AttributeName="EnumeratedAttributeValue"/>

If someone were to create a grammar that mixed upper-case and lower-case
would they have trouble getting people to adopt it?  Is there a
compelling reason to reject a mixed case grammar.  To my eye, mixed case
is more attractive.  It's more like natural English.

So, what are the opinions on each of:
- tag names (lowercase, uppercase, mixed-case)
- attribute names (lowercase, uppercase, mixed-case)
- enumerated attribute values (lowercase, uppercase, mixed-case)

And with each option, are there opinions on any punctuation? Hyphens,
underscores, nothing?

Thanks in advance,

Rob


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