window-size-fixed-p

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

(window-size-fixed-p &optional WINDOW HORIZONTAL IGNORE)

Return non-nil if WINDOW's height is fixed.
WINDOW must be a valid window and defaults to the selected one.
Optional argument HORIZONTAL non-nil means return non-nil if
WINDOW's width is fixed. The optional argument IGNORE has the
same meaning as for `window-resizable'.

If this function returns nil, this does not necessarily mean that
WINDOW can be resized in the desired direction. The function
`window-resizable' can tell that.