static function validate_url_type($slug, $req)
 {
     // validates extra fiedld type that is url
     if ('true' == $req) {
         if (!FSCF_Util::validate_url(self::$form_data[$slug])) {
             self::$form_errors[$slug] = self::$form_options['error_url'] != '' ? self::$form_options['error_url'] : __('Invalid URL.', 'si-contact-form');
         }
     } else {
         if (!empty(self::$form_data[$slug])) {
             if (!FSCF_Util::validate_url(self::$form_data[$slug])) {
                 // was not required but something filled it, so ckeck
                 self::$form_errors[$slug] = self::$form_options['error_url'] != '' ? self::$form_options['error_url'] : __('Invalid URL.', 'si-contact-form');
             }
         }
     }
 }