When using a Simple Refresh or a Smart Refresh windows, the program may receive refresh events, informing it to update the display. See the above discussion for information on when refresh events are sent. A message of the class IDCMP_REFRESHWINDOW arrives at the IDCMP, informing the program of the need to update the display. The program must take some action when it receives a refresh event, even if it is just the acceptable minimum action described below. On receiving a refresh event, BeginRefresh() must be called, then the program should redraw its display, and, finally, call EndRefresh(). The minimum required action is to call the BeginRefresh()/EndRefresh() pair. This allows Intuition and the Layers library keep things sorted and organized.