private static function add_validation_messages($field, array &$add_html)
 {
     if (FrmField::is_required($field)) {
         $required_message = FrmFieldsHelper::get_error_msg($field, 'blank');
         $add_html['data-reqmsg'] = 'data-reqmsg="' . esc_attr($required_message) . '"';
     }
     if (!FrmField::is_option_empty($field, 'invalid')) {
         $invalid_message = FrmFieldsHelper::get_error_msg($field, 'invalid');
         $add_html['data-invmsg'] = 'data-invmsg="' . esc_attr($invalid_message) . '"';
     }
     if ($field['type'] == 'tel') {
         $format = FrmEntryValidate::phone_format($field);
         $format = substr($format, 2, -2);
         $key = 'pattern';
         $add_html[$key] = $key . '="' . esc_attr($format) . '"';
     }
 }