So, we resolved to make user-defined identifiers (like counter-names and namespace prefixes) case-sensitive to avoid dealing with Unicode case-folding and other complications.
This is fine for things that are entirely user-defined, like counters and namespace prefixes, but Tab noticed that it presents a problem when we get to counter-styles: all our styles right now are predefined keywords, and are thus case-insensitive ASCII. When we use @counter-style to define counter styles, we will be allowing users to create their own counter styles. Will those be case-sensitive? What if the user redefines an existing counter-style?
I’d prefer to avoid 1A. because Unicode case-folding is very easy to implement almost-but-not-quite right, and depends on a locale. (Eg. in Python it is tempting to use the 'lower' or 'upper' method of Unicode objects, but these only map codepoints one-to-one and are not proper case folding.)
Resolved on #3.