code: def set_property(self, prop, objects):
          
          self._properties.add(prop)
          objects = set(objects)
          self._objects |= objects
          pairs = self._pairs
          for o in self._objects:
              if o in objects:
                  pairs.add((o, prop))
              else:
                  pairs.discard((o, prop))
docs: Add a property to the definition and set its ``objects``.