private function appendSpineElement(\DOMDocument $document, Spine $spine)
{
$node = $document->createElement('spine');
$node->setAttribute('toc', 'ncx');
foreach ($spine->all() as $item) {
// $child = $document->createElementNS(NamespaceRegistry::NAMESPACE_DC, $item->name, $item->value);
$child = $document->createElement('itemref');
$child->setAttribute('idref', $item->id);
$node->appendChild($child);
}
return $node;
}
