The repaint protocol is the mechanism whereby a program keeps the display up-to-date, reflecting the results of both synchronous and asynchronous events. The repaint mechanism may be invoked by user programs each time through their top-level command loop. It may also be invoked directly or indirectly as a result of events received from the display server host. For example, if a window is on display with another window overlapping it and the second window is buried, a "damage notification" event may be sent by the server. CLIM would then cause a repaint to be executed for the newly-exposed region.
Common Lisp Interface Manager 2.0 User's Guide - 3 Mar 2015