Thank you for your responses. They're very helpful, but I don't think I was clear enough in my initial post. My apologies. What I really would like is an explanations of the "mechanics" of the PERL regex engine in the "unrolling the loop" technique. Why is it more efficient (i.e., no or least amount of backtracking, no infinite or nearly infinite loops, etc.) in the problem situations that some of you have mentioned or in the situation that led Jeffery Friedl to invent it in the first place. Also, this would help me and possibly others understand when its less efficient as respondent Tye has indicated.
Basically, I'm after an understanding of the ghostly depths of what going on at the engine level between the surface dazzle of completing expressions. The fundamentals.