public void set_fullscreen_mode (FullscreenMode mode)
Specifies whether the this should span over all monitors (in a multi-head setup) or only the current monitor when in fullscreen mode.
If the XINERAMA extension is not available or not usable, this function has no effect.
Not all window managers support this, so you can’t rely on the fullscreen window to span over the multiple monitors when ALL_MONITORS is specified.
a toplevel Window