Re: justification/reasoning of tags in XHTML forced to be lowercase?

In the first sentense of XHTML 1.0 point 4, it said XHTML is XML-family
and HTML is SGML-base language, so they must different, XML is case-
sentitive, and the tag defined in DTD of XHTML 1.0 is all lowercase,
that's the reason why XHTML force users to use lowercase... :-)

Funny, because peoples most use lowercase in HTML, XHTML give them the
time to change, from HTML to XHTML, is it the reason ?

> I understand that xml is case sensitive (rather annoying from a language
> perspective, but that is another battle to fight), but I am wondering why
> the XHTML standard is forcing people to use lowercase for their hypertext
> markup tags.  Why not force them to use uppercase?
> 
> What is the justification or reasoning for lowercase tags?