The input protocol Provides the event handler for a sheet. Events may be handled syn-
chronously, asynchronously, or not at all.

The output protocol Provides graphical and textual output, and manages descriptive output
state such as color, transformation, and clipping.

The repaint protocol Invoked by the event handler and by user programs to ensure that the
output appearing on the display device appears as the program expects it to appear.

The notification protocol Invoked by the event handler and user programs to ensure that
CLIM's representation of window system information is equivalent to the display server's.
These protocols may be handled directly by a sheet, queued for later processing by some other
agent, or passed on to a delegate sheet for further processing.