private function _strtoupper($str)
    {
        $str = html_entity_decode($str, ENT_COMPAT);

        if (function_exists('mb_strtoupper')) {
            $str = mb_strtoupper($str, 'UTF-8');
        } else {
            $str = strtoupper($str);
        }

        $str = htmlspecialchars($str, ENT_COMPAT);

        return $str;
    }