window must be kept below other windows. If the
window was already below, then this function does nothing.gdkWindowSetKeepBelow(object, setting)objectGdkWindowsettingwindow below other windowswindow below, if the window
manager supports this operation. Not all window managers support
this, and some deliberately ignore it or don't have a concept of
"keep below"; so you can't 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.
Since 2.4