our $re_true = qr{(?=)}x; our $re_false = qr{(?!)}x; our $count; / # (?{ ... }) or (??{ ... }) or (legacy) (?p{ ... }) \G \( \? (?: \? \?? | p ) (?= \{ ) (?{ local $count = 0; }) (?: \{ (?{ local $count = $count + 1 }) | \} (?{ local $count = $count - 1 }) | \\ . | . )+? (??{ $count == 0 ? $re_true : $re_false }) /xgc;