Overall, +1. But I don't like how disruptive introduction of the classic /regex/ delimiter is. I think something like #regex(...) is a bit too noisy. I would love to keep it as close to the classic delimiter as possible while avoiding the disruption. I prefer what I've already proposed: '/regex/'. I think even #/regex/# is not ideal, as # overshadows /, but I can live with it (especially #/regex/ variant) and prefer it to the disruption.
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