[CSS21] Case-insensitivity not defined

Henri Sivonen brings up the point that ASCII case-insensitivity and
Unicode case-insensitivity are not the same and that we should define
what we want for CSS. For example, should WIDTH and WİDTH match?
WİDTH and width? Should Greek identifiers match case-insensitively
as well? Accented Latin characters? For that matter should 'e' plus
combining acute accent match eacute?

a-z and A-Z need to correspond, but beyond that the use of other
characters in CSS identifiers is limited to mostly to namespace
prefixes and counter names, neither of which are in widespread use.

~fantasai