public function query($capability, $parameter = null)
    {
        $capability = Horde_String::upper($capability);

        if (!isset($this->_data[$capability])) {
            return false;
        }

        return is_null($parameter) ?:
               (is_array($this->_data[$capability]) &&
                in_array(Horde_String::upper($parameter), $this->_data[$capability]));
    }