public function addItem(Item $feedItem)
    {
        if ($feedItem->getVersion() != $this->version)
        {
            $msg = sprintf('Feed type mismatch: This instance can handle %s feeds only, but item for %s feeds given.', $this->version, $feedItem->getVersion());
            throw new \InvalidArgumentException($msg);
        }

        $this->items[] = $feedItem;

        return $this;
    }