There was a decision not to add these to the docs because lay readers mostly find them confusing, because it makes the docs harder to read, and there are no known usability issues with the docs as they are now. So exceptions have been made for functions likes sorted() that have a complex signature that users need to know about. In the case of the math module, we don't get users writing sin(x=pi/4) so these edits are just gratuitous.

Well, the inspect module does very clear distinction:

>>> def foo(x): pass  # like e.g. math.ceil shown in docs
... 
>>> def bar(x, /): pass
... 
>>> inspect.signature(foo)
<Signature (x)>
>>> inspect.signature(bar)
<Signature (x, /)>
>>> foo(x=1)
>>> bar(x=1)  # that's how math,ceil behave in the reality
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: bar() got some positional-only arguments passed as keyword arguments: 'x'

So exceptions have been made for functions likes sorted() that have a complex signature

The os module seems to be one using "/". I doubt that the os.setegid has a complex signature.

Sorry for the nitpick, anyway.