The following behavior seems to be a bug:

* regex '([a-c]+)\1' finds 'abcabc' at offset 0 in text 'abcabc'

That looks correct.

* regex '([abc]+)\1' finds 'bcbc' at offset 1 in text 'abcbc'

That looks correct.

* regex '([a-c]+)\1' finds nothing in text 'abcbc' ???

It should 'bcbc' if you're calling regex_search and nothing if you're calling regex_match. John.