GMC TopKick 2007 Owner's Manual page 50

A rear-facing infant seat (B) provides restraint
with the seating surface against the back of the
infant. The harness system holds the infant
in place and, in a crash, acts to keep the infant
positioned in the restraint.
50
A forward-facing child seat (C-E) provides restraint
for the child's body with the harness and also
sometimes with surfaces such as T-shaped
or shelf-like shields.