Perl has special forces :

Perl maintains a cache of visited states in order to short circuit redundant paths through the NFA, permitting it to evaluate some searches in linear time that take polynomial or exponential time in other Spencer engines.

from "Can Regular Expressions Be Safely Reused Across Languages?": i-programmer.info/programming/perl/13051-can-regular-expressions-be-safely-reused-across-language-boundaries.html