GMC 2008 Savana Van Owner's Manual page 44

Lower Anchors
Lower anchors (A) are metal bars built into the vehicle.
There are two lower anchors for each LATCH seating
position that will accommodate a child restraint with
lower attachments (B).
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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.
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.