GMC 2008 Envoy Denali Owner's Manual page 46

Top Tether Anchor
A top tether (A, C) anchors the top of the child restraint
to the vehicle. A top tether anchor is built into the
vehicle. The top tether attachment (B) on the child
restraint connects to the top tether anchor in the vehicle
in order to reduce the forward movement and rotation
of the child restraint during driving or in a crash.
Your child restraint may have a single tether (A) or a
dual tether (C). Either will have a single attachment (B)
to secure the top tether to the anchor.
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Some child restraints that have a top tether are designed
for use with or without the top tether being attached.
Others require the top tether always to be attached.
In Canada, the law requires that forward-facing
child restraints have a top tether, and that the tether
be attached. Be sure to read and follow the instructions
for your child restraint.
If the child restraint does not have a top tether, one
can be obtained, in kit form, for many child restraints.
Ask the child restraint manufacturer whether or not a
kit is available.
Lower Anchor and Top Tether Anchor
Locations
Second Row
i
(Top Tether Anchor):
Seating positions with top
tether anchors.
j
(Lower Anchor):
Seating positions with
two lower anchors.