Update manual for dynamic docstrings

[malmaud]

No description provided.

[tkelman]

should also mention what sig is for

[malmaud]

I'm actually unclear myself on why you would use it in this context

[tkelman]

@stevengj / @MichaelHatherly? ref #20142 (comment)

[MichaelHatherly]

Passing sig should allow for returning different docs for ?x(1) and ?x(1.0), currently it seems there's a bug in ? mode preventing that from working though.

Probably not hugely important to have for PyCall for example, but I figured it would be best to make "dynamic" docs behave as closely to "normal" ones as possible.

[malmaud]

Ya, that's what I thought initially and then got confused when ?x(1) didn't work. The manual probably shouldn't mention the sig stuff while it isn't actually working.

[kshyatt]

AV failure is in pkg, unrelated. Going to press the pretty button since this is Approved.

[tkelman]

currently it seems there's a bug in ? mode preventing that from working though.

That needs an issue - #20301