Problem: regular expressions don't accept options.

[evoskuil]

https://github.com/imatix/gsl/blob/master/src/ggpcre.c#L129

    rc = pcre_exec (re,
                    NULL,
                    subject-> value. s,
                    (int) strlen (subject-> value. s),
                    0,
                    0,  /* This is the options parameter in the pcre call. */
                    ovector,
                    oveccount);