protected function containsItem()
    {
        $found = false;
        if ($this->hasManifest()) {
            foreach ($this->getManifest()->getElementsByTagName('resource') as $resourceNode) {
                /** @var \DOMElement $resourceNode */
                if ($resourceNode->getAttribute('identifier') == $this->buildIdentifier()) {
                    $found = true;
                    break;
                }
            }
        }
        return $found;
    }