I recently tried to write the look-behind expression (?<=(?:199\d|200\d|\D)) but that results in the error Variable length lookbehind not implemented before HERE mark in regex m/(?<=(?:199\d|200\d|\D)) << HERE /. I got it to work by prepending three dots to ...\D but since I wasn't using any variable quantifiers (question mark, plus, asterisk, etc) I think it should have worked in the first form. So what's the deal here? Even though every component of the alternation was of a known length, because the alternation itself was variable length this didn't work?

In reply to Not-really variable length lookbehind by diotalevi

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