code: def pageId(self, pageId):
          
          if pageId is None:
              return
          if self.mets is None:
              raise Exception("OcrdFile %s has no member 'mets' pointing to parent OcrdMets" % self)
          self.mets.set_physical_page_for_file(pageId, self)
docs: Set the ID of the physical page this file manifests.