screen is an object that represents the known monitor screens.
The width in pixels of the screen.
The height in pixels of the screen.
The screen number.
The number of color planes in the screen.
A list of all of the interfaces visible on the screen.
When the CAPI initializes itself it creates one or more screen objects and they are then used to specify where a window is to appear. A
screen object can also be queried for information that the program may need to know about the screen that it is working on, such as its width, height and depth.
On Microsoft Windows and Cocoa there is exactly one CAPI screen. When there are multiple monitors, there are several rectangles of pixels within the single CAPI screen.
On Motif, there is one CAPI screen for each X11 screen.
In LispWorks for Macintosh 4.3 there is one CAPI screen for each Cocoa screen. In LispWorks for Macintosh 4.4 and later, there is exactly one CAPI screen.
(setq screen (capi:convert-to-screen))
'capi:interface :title "Test")
CAPI User Guide and Reference Manual (Macintosh version) - 3 Aug 2017