GMC 2008 Envoy Denali Owner's Manual page 61

Driver Side shown, Passenger Side similar
The roof-rail airbags for the driver, right front passenger,
and second row outboard passengers are in the
ceiling above the side windows.
CAUTION:
{
If something is between an occupant and an
airbag, the airbag 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.
If your vehicle has roof-rail airbags, never
secure anything to the roof of your vehicle by
routing the rope or tie down through any door
or window opening. If you do, the path of an
inflating roof-rail airbag will be blocked.
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