code: private void onBusHaltChanged(BusItineraryHalt halt) {
  		if (halt.getContainer() == this) {
  			final boolean oldValidity = !ListUtil.contains(this.invalidHalts, INVALID_HALT_COMPARATOR, halt);
  			final boolean currentValidity = halt.isValidPrimitive();
  			if (oldValidity != currentValidity) {
  				if (currentValidity) {
  					ListUtil.remove(this.invalidHalts, INVALID_HALT_COMPARATOR, halt);
  					ListUtil.addIfAbsent(this.validHalts, VALID_HALT_COMPARATOR, halt);
  				} else {
  					this.validHalts.remove(halt);
  					ListUtil.addIfAbsent(this.invalidHalts, INVALID_HALT_COMPARATOR, halt);
  				}
  				checkPrimitiveValidity();
  			}
  		}
  	}
docs: ----------------------------------------------