It's a backreference to the first capture group, which is denoted by the first s... | Hacker News

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		tlrobinson on Nov 30, 2014 \| parent \| context \| favorite \| on: Regex Crossword It's a backreference to the first capture group, which is denoted by the first set of parenthesis, e.x. `(.)+\1` would match "ABAB", or "ABCABC", etc. "\2" would match the second capture group, e.x. `(.)(.*)\2\1` would match "ABBA", or "AABBBBAA", etc.

Edmontonian on Nov 30, 2014 [–]

so in your first example, "AB" was in the capture group and the \1 repeats it?

tlrobinson on Nov 30, 2014 | [–]

Correct. The following

    (.*)\1+

Would also match "ABABAB", for example.

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