code: def url(self, url):
          
          if url is None:
              return
          el_FLocat = self._el.find('mets:FLocat', NS)
          if el_FLocat is None:
              el_FLocat = ET.SubElement(self._el, TAG_METS_FLOCAT)
          el_FLocat.set("{%s}href" % NS["xlink"], url)
docs: Set the ``xlink:href`` of this file.