http://www.perlmonks.org?node_id=762846


in reply to Regex bug in 5.10 (was: Using Look-ahead and Look-behind)
in thread Using Look-ahead and Look-behind

...which (in pre-5.10) will output empty strings every time.

With 5.10.0, /(?=(.*?))/g; outputs one empty string.  And I can confirm the behavior reported by jds17 with /(?=(.*))/g.