A coordinate system Provides the ability to refer to locations in a sheet's abstract plane.

A region Defines an area within a sheet's coordinate system that indicates the area of interest
within the plane, that is, a clipping region for output and input. This typically corresponds
to the visible region of the sheet on the display.

A parent A sheet that is the parent in a windowing relationship in which this sheet is a child.

Children An ordered set of sheets that are each a child in a windowing relationship in which
this sheet is a parent. The ordering of the set corresponds to the stacking order of the
sheets. Not all sheets have children.

A transformation Determines how points in this sheet's coordinate system are mapped into
points in its parents.

An enabled flag Indicates whether the sheet is currently actively participating in the window-
ing relationship with its parent and siblings.

An event handler A procedure invoked when the display server wishes to inform CLIM of
external events.

Output state A set of values used when CLIM causes graphical or textual output to appear
on the display. This state is often represented by a medium.

6.3 Sheet Protocols
A sheet is a participant in a number of protocols. Every sheet must provide methods for the
generic functions that make up these protocols. These protocols are:

The windowing protocol Describes the relationships between the sheet and its parent and
children (and, by extension, all of its ancestors and descendants).