code: def serialize(self, fully_qualified=True):
          
          now = datetime.utcnow().replace(microsecond=0).isoformat("T")
          files = self.all_files()
          mdsecs = self._collect_mdsec_elements(files)
          root = self._document_root(fully_qualified=fully_qualified)
          root.append(self._mets_header(now=now))
          for section in mdsecs:
              root.append(section.serialize(now=now))
          root.append(self._filesec(files))
          root.append(self._structmap())
          root.append(self._normative_structmap())
          return root
docs: Returns this document serialized to an xml Element.
  
          :return: Element for this document