Matthew, Guido wrote "check that the whole input string matches" (or slice if pos and (possibly also) endpos is/are given).  So, yes, \Z is more to the point than $ if people want to continue wasting time trying to implement this as a Python-level function ;-)

I don't understand what you're asking about MULTILINE.  What's the issue there?  Focus on Guido's "whole input string matches", not on his motivational talk about "a regex ending in $".  $ and/or \Z aren't the point here; "whole input string matches" is the point.