Python, for all its power and popularity, has long lacked a form of flow control found in other languages—a way to take a value and match it elegantly against one of a number of possible conditions.

I also just realized that I sort of sketched the basics of "algebraic matching", where the original PEP completely bypassed that issue and (x, x) doesn't even do what seems obvious? Or am I reading ...

That is pretty self-explanatory except perhaps for "_", which is a wildcard that will match anything. The idea is that each case will be tried in the order specified, the first to match will be ...