protected function _parseConfig($conf, $stack_name = 'global')
    {
        if (is_string($conf)) {
            $this->_parseConfigRecursive($conf, null, $stack_name);
        } elseif (is_array($conf)) {
            array_walk_recursive($conf, array($this, '_parseConfigRecursive'), $stack_name);
            $conf = array_filter($conf);
        }
        return $conf;
    }