What are the backstroke rules during the race?

Under World Aquatics rules (Part Two, Article 6):

• Start: swimmers line up in the water facing the starting end, both hands on the grips. No standing in or on the gutter or curling toes over its lip. With a backstroke ledge, at least one toe of each foot must touch the wall or touchpad face, and toes may not curl over the top of the touchpad.
• At the start and after each turn the swimmer must push off and swim on the back throughout, except during the turn.
• "On the back" includes a roll of up to, but not including, 90 degrees from horizontal. Head position doesn't matter.
• Some part of the body must break the surface throughout, except during the turn and for up to 15 m after the start and each turn; the head must be up by 15 m.
• Finish: touch the wall on the back. The swimmer may be completely submerged once the head has passed the 5 m mark before the finish.