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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def serialize(self, fully_qualified=True):
 """ Returns this document serialized to an xml Element. :return: Element for this document """

        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