I just did a quick test to confirm the behavior. I don't see it mentioned in the docs for pos, but I guess the reason would be that you're doing a substitution, so the matched text is essentially considered removed from the string at that point. Therefore pos will return the position where the substituted value will be inserted once you've computed it.

In reply to Re: Inconsistent behaviour of pos() in s/ ... / ... / by Errto
in thread Inconsistent behaviour of pos() in s/ ... / ... / by johngg

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