Chris,
   I first verified the issue then created some wording and you pointed out that we needed test cases so I created a bunch of test cases.  As you pointed out "I count 2*3*2=12 possibilities to check (excluding src and dst being on different filesystems):" so I created 16 test cases then discovered that the behavior is different on Windows and Unix so all together there are 32 test cases.  Your last comment about the test cases being "Dry" didn't make sense to me.  If you provide specific feedback I would be glad to work on the issue.  The test cases are designed to make sure that the documented behavior is actually how Python performs.  It made the most sense to me to put together two patches one for the test cases and another for the documentation, but maybe that has confused everybody?  If it would help I could submit a single patch.  OSRenameCombinations.py was just for reference to prove to myself that I got all the possible test cases.

I am a fairly new Python contributor and this is my first attempt at writing test cases so I could be missing something.  Thanks for the mentorship and the time required for a little extra guidance.