In https://github.com/whatwg/html/issues/1666 we are discussing whether we can remove the spec's use of "compatibility caseless" matching for radio groups and image maps. "Compatibility caseless" is a type of Unicode case-insensitive matching. It turns out that nobody actually implements "compatibility caseless" exactly, but Chrome, Firefox, and Edge all do implement some form of Unicode case-insensitive matching.

WebKit does completely case-sensitive matching for radio groups, but not for image maps.

It would be good to add use counters to see how often Chrome sees radio button names and image map hash names that are deemed "the same", but are not byte-for-byte equal. If this happens rarely, we can just move to case-sensitive matching in the spec and in Chrome, thus matching WebKit and simplifying everything.