GMC 2008 Yukon Denali Owner's Manual page 60

Child Restraint Systems
The harness system holds the infant in place and, in a
crash, acts to keep the infant positioned in the
restraint.
1-56
A rear-facing infant
seat (A) provides restraint
with the seating surface
against the back of
the infant.
A forward-facing child
seat (B) provides restraint
for the child's body
with the harness.