public function set($key, $value)
    {
        $key = trim($key, '.');
        if (strpos($key, '.') !== false) {
            $array =& $this->_items;
            foreach (explode('.', $key) as $v)
                $array =& $array[$v];
            $array = $value;
        } else {
            $this->_items[$key] = $value;
        }
    }