Sheets have the following properties:
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 children 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' coordinate system.
An enabled flag--Indicates whether the sheet is currently actively participating in the windowing 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.
Common Lisp Interface Manager 2.0 User's Guide - 7 Aug 2017