http://www.perlmonks.org?node_id=1018767


in reply to Re: A regex that only matches at offset that are multiples of a given N?
in thread A regex that only matches at offset that are multiples of a given N?

In this regex:
fred (? (?{ pos % 4 != 0 }) (?!) ) (....)

What does this construct do:

(?stuff)

I can't find anything about that in perlre.

Edit: Ah, the boolean test finally clued me in:

(?(condition)yes-pattern)