How does non-backtracking subexpression work "(?>exp)"
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I am trying to become better at regular expressions. I am having a hard time trying to understand what does `(?> expression )` means. Where can I find more info on non-backtacking subexpressoins? The description of [THIS][1] link says:

> Greedy subexpression, also known as a non-backtracking subexpression.
> This is matched only once and then does not participate in
> backtracking.

this other link: http://msdn.microsoft.com/en-us/library/bs2twtah(v=vs.71).aspx has also a definition of non-backtracking subexpression **but I still am having a hard time understanding what it means plus I cannot think of an example where I will use `(?>exp)`**


  [1]: http://www.codeproject.com/Articles/9099/The-30-Minute-Regex-Tutorial