Fundamentally there’s nothing wrong with it, but if I had to implement a installer or a resolver, then this is a special case I have to be aware of when parsing the package metadata. Clearly some code was necessary to add this behavior in pip (version 21.2 as Hyneck claims). Anyways, we can agree to disagree else we go into this rabbit hole too much.
Okay, so I’m convinced there is no documentation of this specifically. I think it’s needed. I will take this request elsewhere.