Is there a description of how __cmp__ works for dict objects in Python 2?

I've been trying to make a dict subclass inheriting from UserDict.DictMixin that supports non-hashable keys. Performance isn't a concern. Unfortunately, Python implements some of the functions in DictMixin by trying to create a dict object from the subclass. I can implement these myself, but I am stuck on __cmp__.

I cannot find a succinct description of the logic used by the built-in __cmp__ for the dict class.