“Decorations” are the features the window manager adds to a toplevel gdk.Window This function sets the traditional Motif window manager hints that tell the window manager which decorations you would like your window to have. Usually you should use Window.setDecorated on a gtk.Window instead of using the GDK function directly.
The decorations argument is the logical OR of the fields in the GdkWMDecoration enumeration. If GDK_DECOR_ALL is included in the mask, the other bits indicate which decorations should be turned off. If GDK_DECOR_ALL is not included, then the other bits indicate which decorations should be turned on.
Most window managers honor a decorations hint of 0 to disable all decorations, but very few honor all possible combinations of bits.