display-backing-store

display-backing-store is a compiled Lisp function in `frame.el'.

(display-backing-store &optional DISPLAY)

Return the backing store capability of DISPLAY's screen.
The value may be `always', `when-mapped', `not-useful', or nil if
the question is inapplicable to a certain kind of display.
DISPLAY can be a display name or a frame.
If DISPLAY is omitted or nil, it defaults to the selected frame's display.