My first thought for an "easy solution" is to generate a reversed version of the target string if there is a variable length look behind, then use the usual look ahead match processing on the reversed string starting at the "reversed" anchor point.

True laziness is hard work

In reply to Re^3: Why is variable length lookahead implemented while lookbehind is not? by GrandFather
in thread Why is variable length lookahead implemented while lookbehind is not? by Kc12349

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