gdk-window-set-keep-below (window setting)

window -- a toplevel gdk-window object
setting -- a boolean whether to keep window below other windows

Set if the window must be kept below other windows. If the window was already below, then this function does nothing.

On X11, asks the window manager to keep the window below, if the window manager supports this operation. Not all window managers support this, and some deliberately ignore it or do not have a concept of "keep below"; so you cannot rely on the window being kept below. But it will happen with most standard window managers, and GDK makes a best effort to get it to happen.