code: def to_xml(self, xmllint=False):
          
          root = self._tree.getroot()
          ret = ET.tostring(ET.ElementTree(root), pretty_print=True)
          if xmllint:
              ret = xmllint_format(ret)
          return ret
docs: Serialize all properties as pretty-printed XML
  
          Args:
              xmllint (boolean): Format with ``xmllint`` in addition to pretty-printing