Reading the code, when I saw the commend saying All letters used in the representation are normalized to lowercase, I thought it also refers to hex letters. However, a few lines later, I was disappointed to see Change hex literals to upper case..

There's one practical issue with use of upper-case hex letters, though, and that's similarity between letter B and digit 8.

I have seen bugs caused by this similarity in security-sensitive code, such as UTF-8/-16 decoders. Personally, I always used uppercase letters in hex numerals prior to that incident, because of the aesthetics of it; but, since then, have been switching to lowercase anywhere possible.

Maybe Black would consider switching to lowercase hex letters, as well?