public function extract($parts = null) {
        if ($this->isEmpty()) {
            return false;
        }

        if ($parts === null) {
            return $this->content;
        }

        if (is_array($parts)) {
            $result = array();
            foreach ($parts as $key) {
                if (isset($this->content[$key])) {
                    $result[$key] = $this->content[$key];
                }
            }

            return $result;
        }

        return isset($this->content[$parts])?$this->content[$parts]:false;
    }