private void InitializeXDocumentNode()
{
if (_xDocumentNode != null) return;
IEnumerable<XElement> elements = XDocument.Descendants(xsfNamespace + xDocumentClass);
foreach (XElement element in elements)
{
if (_xDocumentNode != null) throw new ArgumentException("Manifest has multiple xDocumentClass nodes");
_xDocumentNode = element;
}
}