This function can be called to determine if a Window is using client-side decorations which is indicated by the _GTK_FRAME_EXTENTS X11 atom.
It furthermore sets a pointer of type Border to the actual extents.
| window |
A Window |
| extents |
A pointer to a Border to copy to. |
|
TRUE if a Window has the _GTK_FRAME_EXTENTS atom set. |