What does AC 120-91 add to these requirements?

AC 120-91 introduces an expanding obstacle clearance corridor:

• For straight-out departures, the corridor begins expanding 4,800 feet from the runway end at a rate of 0.0625 × distance, up to a maximum half-width of 2,000 feet.
• For turning departures (track change >15°), the corridor expands from the start of the turn at a rate of 0.125 × distance, up to a maximum half-width of 3,000 feet.