code: def _track_tendril(self, tendril):
          
  
          self.tendrils[tendril._tendril_key] = tendril
  
          # Also add to _tendrils
          self._tendrils.setdefault(tendril.proto, weakref.WeakValueDictionary())
          self._tendrils[tendril.proto][tendril._tendril_key] = tendril
docs: Adds the tendril to the set of tracked tendrils.