window_add_callback_c

	callback_id.i2.v = window_add_callback_c(type.i4.v, callback_func.f.v,
						 callback_data.g.v,
						 handle.i1a.r)

	This function will register the routine "callback_func" with the
	TV window management routines for notification in the event
	of window modifications.

	type		type of callback
			(WMNGR_PRE_CREATE_CALLBACK -> callback is invoked just
						      before a window is
						      created,
			 WMNGR_CREATE_CALLBACK -> callback is invoked after
						  a window is created,
			 WMNGR_CHANGE_CALLBACK -> callback is invoked when
						  a window is modified,
			 WMNGR_PRE_DELETE_CALLBACK -> callback is invoked just
						      before a window is
						      deleted,
			 WMNGR_DELETE_CALLBACK -> callback is invoked after
						  a window is deleted,
			 WMNGR_DELETE_REQUEST_CALLBACK -> callback is invoked
							  if a window delete
							  request is made,
			 WMNGR_CHANGE_PARAM_CALLBACK -> callback is invoked
							if a global parameter
							is modified)
	callback_func	address of function to be called as follows:
			callback_func(wid.i2.v, type.i4.v, callback_data.g.v,
				      window_data.s.r)
			("window_data" is a structure which is dependent
			 on the action generating the callback having the
			 following types:
			 WINDOW_CREATE_CALLBACK_DATA -> window creation,
			 WINDOW_CHANGE_CALLBACK_DATA -> window modification or
							global parameter
							modification,
			 WINDOW_DELETE_CALLBACK_DATA -> window deletion,
			 WINDOW_DELETE_REQUEST_CB_DATA -> window deletion
							  request)
	callback_data	pointer to user-supplied data to be passed to
			callback function
	handle		null terminated handle string for identification
			purposes

	This function returns status values as follows:

	CBS_INVARG		invalid callback type requested
	CBS_MEMFAIL		dynamic memory allocation failure
	otherwise		callback ID

	This function requires the following include files:

	cns_data_structs_h, cbslib_h, acnet_errors_h

	Related functions:

	window_remove_callback_c, window_construct(_c), window_set_parameter_c,
	window_set_handle_c, window_request_delete_c, window_callback_init,
	window_callback_term, window_register_function_c,
	window_unregister_function_c, intro_tv_windows

	C/C++ usage:

	static const char	handle[] = "my_callback";
	short	callback_id;
	int	type = WMNGR_CREATE_CALLBACK;
	void	callback_func(short window_id, int type, void *callback_data,
			      WINDOW_CREATE_CALLBACK_DATA *window_data);
	void	*callback_data = (void *) NULL;

	callback_id = window_add_callback_c(type,callback_func,callback_data,
					    handle);