prompt: kill matchflags
Python already lets one to embed RE flags directly in a regex, which
is a much nicer way to do things:
(?iLmsux)
(One or more letters from the set "i", "L", "m", "s", "u", "x".)
...
matchflags was introduced in
67afecb8d6cc, and the record extension is the only
user. I've killed matchflag, and adjusted record code appropriately.