Hey folks.

ZWJ, and variations selectors seem to have been added to XID_Continue as of Unicode 15.1,

despite UAX31 recognizing that "The use of default-ignorable characters in identifiers is problematic".

The solution to that is to define that we implement the Default-Ignorable Exclusion Profile,

which I believe restores the Unicode 15 / C++23/ SG16 consensus on Identifier grammar behavior.

It is very surprising to me that ZWJ is opt-out rather than opt-in given the security implications and the fact supporting them requires implementation of TR39 3.1.1.

I suppose this was done to better support Sanskrit?

Anyway, it might be useful to either:

- Mandate the Default-Ignorable Exclusion Profile

- Mandate some form of TR39 conformance (wich is going to be quite the burden for implementers given our bandwidth)

- Or allow/recommend either of the above options.

Thanks,

Corentin