A global instance of this class is created at the very beginning of the program, before any UIObject's are created. It is initially empty, but each time a new UIObject is started, the global instance is specified in the UIObject constructor and that UIObject will register itself with the list.
This object is used primarily in the main event loop of VMD to cause all the interface components to check for events, and in the CommandQueue object to inform components when an action occurs. It is also used by parts of the program that need a list of the names of UIObject's.