There are no standard sheet classes in CLIM, and no pre-packaged way to create sheets in general. If a programmer needs to create an instance of some class of sheet, make-instance must be used. In most cases, application programmers will not deal with sheets directly, but instead will use a subclass of sheets known as panes. Panes can be created by calling the make-pane function. For a more detailed discussion on panes, see Chapter 10, Panes and Gadgets
sheet [Protocol Class]
Summary: The protocol class that corresponds to a sheet, a subclass of
rectangle . If you want to create a new class that behaves like a sheet, it should be a subclass of sheet . Subclasses of sheet must obey the sheet protocol.
All of the subclasses of sheet are mutable.
Summary: Returns t if object is a sheet; otherwise, it returns nil .
Summary: The basic class on which all CLIM sheets are built, a subclass of sheet . This class is an abstract class intended only to be subclassed, not instantiated.
Common Lisp Interface Manager 2.0 User's Guide - 7 Aug 2017