GMC Envoy Owner's Manual page 59

If your vehicle has a roof-mounted airbag for the right
front passenger and the person directly behind that
passenger, it is located in the ceiling above the
side windows.
1-52
CAUTION:
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If something is between an occupant and an
airbag, the bag might not inflate properly or it
might force the object into that person causing
severe injury or even death. The path of an
inflating airbag must be kept clear. Do not put
anything between an occupant and an airbag,
and do not attach or put anything on the
steering wheel hub or on or near any other
airbag covering. And, if your vehicle has
roof-mounted airbags, never secure anything
to the roof of your vehicle by routing the rope
or tiedown through any door or window
opening. If you do, the path of an inflating side
impact airbag will be blocked. The path of an
inflating airbag must be kept clear.