Depends on what you mean by "built in" or "core module". It'll ship as part of the standard Parrot distribution since so many languages that do regexes do perl 5 compatible ones, so it seems foolish to have three or four different perl 5 regex compilers. It'll be an add-on parser module, probably loaded on demand. (Though you won't have to have a use perl5 qw(re); in your program anywhere) If it's small enough, it might just get yanked in unconditionally.