Perl flip-flop seems to be a generalization of range matching like in awk, sed, SNOBOL and others.* (Generally "rule-action" languages.)

I can see where the generalization may have gone too far, but in the context of regular expressions, syntax like:

seems clear to me. Or perhaps the awk/sed syntax:

might be clearer - except that it would be inconsistent with other uses of , in Perl.

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* I learned about SNOBOL long ago when I took a "300 level" CS class called "Language Stuctures". It was a very interesting class. Learned about several weird languages, including ProLog, LISP and APL.