When * is changed to ^, it does not work either. Why are you changing it at all?

But jokes aside: The *? matches after seeing the first occurence of AATT, so there are no dupes. The {50,100} must match at least 50 times, so if there is AATT after say 25^th character, it cannot stop there and must match a larger string.

Use YAPE::Regex::Explain to see what your regular expresions mean.

Moreover, you are replying to a node that is not related to your question.