How would you redefine Perl regexes to do this?

But the  (?:[^\1]*) construct was envisioned to get around the lack of variable-width positive/negative lookbehind; I think I'd just implement that. (Of course, I suspect the reason it hasn't been implemented yet is because it's a royal pain to do so. Perhaps best to be careful what you wish for lest you find yourself with a new and very difficult assignment. As for implementing ferkcabs, I think I'd switch to another profession first. :)