I haven't looked at anything in this PR, so just popping in to confirm that the first time I saw stuff like:

    len(obj, /)

in the docs I had no idea at all what it was trying to say.  I thought it was a typo.

Also the second, third, fourth, ..., times I saw it.

However, because Python didn't _accept_ that syntax in my own function definitions, that may well have made it extraordinarily hard to figure out.

If the syntax is going to be accepted now, that does change things to my eyes.  It becomes a question of discoverability then.

I'll note that Googling on

    python slash in formal argument list

turns up an excellent Stackoverflow explanation as its top hit for me today, although not if "slash" is replaced with "/".