The lexer documentation says that the u prefix works on strings since 3.3, but doesn't explain what or how, which is all the more problematic since it explicitly mentions difference from the behavior documented in Python 2.

It also doesn't specify the ELLIPSIS token or the <> future token mentioned in the grammar (that should probably be removed, for PEP 401 is a joke — unless that's intentional, in which case a smiley might be useful).

https://docs.python.org/3.5/reference/lexical_analysis.html