Window.setDecorated

By default, windows are decorated with a title bar, resize controls, etc. Some [window managers][gtk-X11-arch] allow GTK+ to disable these decorations, creating a borderless window. If you set the decorated property to false using this function, GTK+ will do its best to convince the window manager not to decorate the window. Depending on the system, this function may not have any effect when called on a window that is already visible, so you should call it before calling [gtk.widget.Widget.show].

On Windows, this function always works, since there’s no window manager policy involved.