GMC Jimmy 2004 Owner's Manual page 44

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.
1-38
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.