This is a port of the glibc gnu regex engine into perl. There are few reasons
you would need this. The few I can think of include:

0) You wish to use untrusted user expressions in such a way as to be able to
catch errors. Example: eval { alarm 2; m/((){1024}){1024}/ } is an instant
uncatchable segmentation fault. GNU's regexps will still fail, but in a timeout
way rather than an instant segfault way.

1) You wish to have POSIX compliance on ... something ... Perl's regexps are
slightly different -- arguably better, but different.


( ... if you think of anything else, let me know, since reason 0 evaporates under 5.9.3+ ... )