Documentation

Currently, the only way to get up to date information on the type parameters and their variance for classes in collections.abc is to look at the source code of typeshed. I think it would be helpful to add that information to https://docs.python.org/3/library/collections.abc.html. For example, it could be something like

class collections.abc.Iterable[covariant T]

ABC for classes that provide the __iter__() method....
For type checking purposes, this class is considered a protocol, so assignability is checked structurally, not nominally.

class collections.abc.MutableMapping[invariant K, invariant V]
class collections.abc.Mapping[invariant K, covariant V]
ABCs for read-only and mutable mappings.
The key parameter is invariant in Mapping because <...>

(perhaps the variance words could link to the right place in the documentation describing these terms, for people unfamiliar with variance)

I'd like to work on that if possible. The specific way in which this information is presented might need to be discussed first.