"X" is the lenght of the text (when matching one text against more than one regular expression). Read the full paper and you'll understand.
This specific engine still very specialized. But the technique used on it is more general than the Perl's current implementation and innovative, and deserves a deeper study, and maybe even a implementation.
I'm thinking seriously on volunteering. I believe that such a work could help me achieve a MSc degree (and this is very desirable) while still contributing to the Perl Community. I'm looking for someone with time and patience enough to guide me. Maybe you're interested.
Send a patch to the Perl source code stills on my computer dreams list. :-) I'll send a good one someday.