2003 GMC Envoy Owner's Manual - Page 117

Rear Compartment Storage PaneKover Your vehicle may have this feature. Insert the front corners of the panel into the top guides and slide the panel forward. Press down on the back of the panel to lock it in place. This acts as a cargo shade. If you were to carry things onthe adjustable shelf when it is in the upper (cargo cover) position, then during a sudden vehicle movement or a crash those things could be thrown around in the vehicle. You or others could be injured. When it is in the upper position, always secure any cargo on the floor beneath the shelf/cover. Upper Position 2-48