Perl-compatible regular expressions are not semantically equivalent to real regular expressions (as the article seems to claim). In fact, they correspond to com

Perl-compatible regular expressions are not semantically equivalent to real regular expressions (as the article seems to claim). In fact, they correspond to completely different grammars in the Chomsky hierarchy. PCREs are Turing complete (and for closely related reasons, extremely slow for some expressions), while regular expressions are isomorphic to FSMs (which are always linear time in the length of their input).