The documentation of Python 2.6 and 2.7 only mentions the class
attribute "__mro__" in ABC documentation and in Data model documentation
when explaining description invocation (see search results:
http://docs.python.org/dev/search.html?q=__mro__&check_keywords=yes&area=default)

Imho __mro__ lacks documentation in "Standard Type Hierachy", where
special attributes of fundamental data types are documented.