When securing a child in the Backless Booster Seat mode, what are the key points I need to remember?

Ensure that your child's ears do not extend above the top of the vehicle seat back or headrest. Buckle the vehicle’s lap and shoulder belt system properly behind armrests with the lap portion lying low across hips and the shoulder belt positioned between neck and edge of shoulders, avoiding gaps by using belt guides if necessary. Follow section 5-C for precise instructions.