protected function _mergeConfig($current, $successor)
    {
        if (is_array($current) and is_array($successor)) {
            foreach ($successor as $key => $value) {
                if (isset($current[$key])
                    and is_array($value)
                    and is_array($current[$key])) {

                    $current[$key] = $this->_mergeConfig($current[$key], $value);
                } else {
                    $current[$key] = $successor[$key];
                }
            }
        }
        return $current;
    }