This module is intended to test your regular expressions. Given a subject
string and a regular expression (a.k.a. pattern), the module not only tests
whether the regular expression completely matches the subject string, it
performs a utf8::upgrade or utf8::downgrade on the subject string and
performs the tests again, if necessary. Furthermore, given a pattern with
capturing parenthesis, it checks whether all captures are present, and in the
right order. Both named and unnamed captures are checked.