My Second Edition Camel book appears to have no mention of this feature... is it new to Perl 5.6, or just one of those details left out of the Camel? I suppose that the third possibility would be that it is in the Camel and I was too dumb to notice, but let's not talk about that.
It looks pretty darn useful though, as merlyn illustrated... I'm surprised that I've never heard of it before.