The \1 is a backreference and will match the same thing that the first parenthesis matched. It isn't all that useful in this example since it could be rewritten as /(is) is/ but something like /(\d)\1/ would match on the same number twice in a row (because the \1 matches the same number that was found with the (\d)), thinking up more useful examples will be an exercise left up to the reader.

In reply to Re: Code Explaining by nardo
in thread Code Explaining by Anonymous Monk

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