Wow - what a cool use of local variables in regex code expressions! And it shows, IMO by far the best way to create complex regexes: machine generate them a bit at a time for good comprehension.

This sort of approach to backtracking fits naturally into the perl6 regex overhaul. Although ease of parsing complex grammars will be the most obvious benefit of perl6 rules, I think associated temp variables synchronized with backtracking will provide a powerful tool for algorithms such as this.

Thanks Abigail-II!

-Mark