window-preserve-size

window-preserve-size is a compiled Lisp function in `window.el'.

(window-preserve-size &optional WINDOW HORIZONTAL PRESERVE)

Preserve height of window WINDOW.
WINDOW must be a live window and defaults to the selected one.
Optional argument HORIZONTAL non-nil means preserve the width of
WINDOW.

PRESERVE t means to preserve the current height/width of WINDOW's
body in frame and window resizing operations whenever possible.
The height/width of WINDOW will change only if Emacs has no other
choice. Resizing a window whose height/width is preserved never
throws an error.

PRESERVE nil means to stop preserving the height/width of WINDOW,
lifting the respective restraint induced by a previous call of
`window-preserve-size' for WINDOW. Calling `enlarge-window',
`shrink-window', `split-window' or `fit-window-to-buffer' with
WINDOW as argument also removes the respective restraint.

Other values of PRESERVE are reserved for future use.