clang claims to implement this but that doesn't seem to be the case, I think
const char *p = R"abc`@$(foobar)abc`@$";
should be accepted for -std=c++2c.
I'm lost at what we need to do for
This is currently rejected by GCC ‘error: universal character is not valid in an identifier’, although this seems to be a bug, and the code is accepted by clang and msvc.
in the paper (3.1).