From: Nathan <njmacinnes@...>
Date: 2010-04-09T17:40:01+09:00
Subject: zero-width positive "look-behind"?

> "tttttattttt".match(/ttt(?=a)/) # http://rubular.com/r/21Zo6JP09f
=> ["ttt"]
> "tttttattttt".match(/(?=a)ttt/) # http://rubular.com/r/d1VSUwwZUu
=> nil

Why? And how can I get this effect?