Backreferences

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Matching Same Text Again & Again

([a-z]\w\s\W\d\D[A-Z][a-zA-Z][aeiouAEIOU]\S)\1

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Backreferences to Failed Groups

You have a test string S. Your task is to write a regex which will match S, with following condition(s):

• S consists of 8 digits.

• S may have "-" separator such that string S gets divided in 4 parts, with each part having exactly two digits. (Eg. 12-34-56-78)

^\d{2}(-?)\d{2}\1\d{2}\1\d{2}$

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Branch Reset Groups

^\d{2}(-(?:--)?|\.|:)\d{2}\1\d{2}\1\d{2}$

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Forward References

^(\2tic|(tac))+$