The CAR class adds the Beep horn item to its primary pop-up menu by overriding wpModifyPopupMenu inherited from WPObject. The method override for wpModifyPopupMenu calls wpInsertPopupMenuItems, also inherited from WPObject, to insert the item into the CAR's pop-up menu.

The CAR class also adds the Open car item (OPEN_CAR) to its Open submenu by overriding wpModifyPopupMenu. The method override calls wpInsertPopupMenuItems to insert Open car into the Open submenu.