So the current (after the aforementioned commit) form of the description is:

   A dotted lookup such as ``super(A, a).x`` searches
   ``obj.__class__.__mro__`` for a base class ``B`` following ``A`` and then
   returns ``B.__dict__['x'].__get__(a, A)``.  If not a descriptor, ``x`` is
   returned unchanged.

I guess here ``obj`` was supposed to be ``a``.

But is the description correct when it comes to what class is used where?
I.e., shouldn't it be rather something along the lines of the following:

   A dotted lookup such as ``super(A, obj).x`` (where ``obj`` is an
   instance of ``A`` of some other subclass of ``A``) searches
   ``A.__mro__`` for a base class ``B`` whose `__dict__` contains name
   ``"x"`` and then returns ``B.__dict__['x'].__get__(obj, type(obj))``.
   If ``B.__dict__['x']`` is not a descriptor, it is returned unchanged.

***

Ad my comment #2 -- yes, it became groundless with time... Minor explanation: when I reported this issue in 2015, the signature of `object.__get__` was documented just as "__get__(self, instance, owner)" (see: https://docs.python.org/3.5/reference/datamodel.html#implementing-descriptors); that's why I wrote about an inconsistency.