LPM: Lookahead assertions

[Rich Bowen]

Can someone adequately explain to me the lookahead assertion in regex? If that
is indeed what they are called - the ?: notation on the beginning of a regex.

I'm working on the reefknot code (http://www.reefknot.org/) and there are a
number of regex that have this in them, aren't working the way that I expect
them to, and I can't really figure out what's going on.

Examples would be nice too. I'll post the offending code if you like, but it's
kinda gruesome, and I'm not sure if it serves to illustrate or muddy.

-- 
As we trace our own few circles around the sun
We get it backwards and our seven years go by like one
	Dog Years (Rush - Test for Echo - 1999)