I think documenting this make sense, I will point out that I believe the gcc documentation is could be improved on in many ways. It does not explicitly mention this is undefined behavior in C++, it follows from it being UB that it is not standard conformant but it is probably worth it to explicitly say so.
I think it would be more helpful to not say there are standards conforming alternatives even if this not elaborated on.
This does not have to be a deep research project to document but we can improve on the level of details provided in the gcc docs.