Steven, thanks for noticing the docs!  I was surprised to hear it wasn't documented, but not surprised enough to check myself ;-)

This decision was suggested by me, and endorsed by Guido, when designing timsort looking ahead to Python 3, where __cmp__ was going to vanish.  The convenience of needing to add only a single method to support a custom sort order is considerable.

Since it's working as designed and dccumented, and I know for certain that code in the wild relises on it, I'm inclined to reject this report.  However, rather than add more words to `sorted()`, I'd suggest removing words from `sorted()`, pointing instead to the `.sort()` docs for all specification of `sorted()`'s sorting behavior.