if ((temp = hv_fetch(spec, "regex", 5, 0))) {
        dSP;

        IV has_regex = 0;
        IV ok;

        SvGETMAGIC(*temp);
        if (SvPOK(*temp)) {
            has_regex = 1;
        }
        else if (SvROK(*temp)) {
            SV* svp;

            svp = (SV*)SvRV(*temp);

            #if PERL_VERSION <= 10
            if (SvMAGICAL(svp) && mg_find(svp, PERL_MAGIC_qr)) {
                has_regex = 1;
            }
            #else
            if (SvTYPE(svp) == SVt_REGEXP) {
                has_regex = 1;
            }
            #endif
        }

        if (!has_regex) {
            SV* buffer;

            buffer = sv_2mortal(newSVpv("'regex' validation parameter for '", 0));
            sv_catsv(buffer, get_called(options));
            sv_catpv(buffer, " must be a string or qr// regex\n");
            FAIL(buffer, options);
        }

##</code><code>##

PV_TEST_PERL=1 perl script.pl

##</code><code>##

BEGIN { $ENV{PV_TEST_PERL} = 1; }