public function registerDocument($document, NodeInterface $node, $locale)
    {
        $oid = $this->getObjectIdentifier($document);
        $uuid = $node->getIdentifier();

        // do not allow nodes without UUIDs or reregistration of documents
        $this->validateDocumentRegistration($document, $locale, $node, $oid, $uuid);

        $this->documentMap[$oid] = $document;
        $this->documentNodeMap[$oid] = $uuid;
        $this->nodeMap[$node->getIdentifier()] = $node;
        $this->nodeDocumentMap[$this->getNodeLocaleKey($node->getIdentifier(), $locale)] = $document;
        $this->documentLocaleMap[$oid] = $locale;
    }