Message 344246 - Python tracker

Guido, I remember you were against exposing `ForwardRef` as public at some point, but recently you approved https://github.com/python/cpython/pull/13456 that added it to `typing.__all__`. I don't have any particular opinion on this, but if you don't object, I think it would make sense to add a short section about this to the docs, since it may be exposed at runtime, e.g. in `List['Cls']`.