What is the function of the 'Kneeling' system (Absenkeinrichtung) on modern low-floor passenger transit buses?

1. It pneumatically lowers the right side of the bus chassis by several centimeters at bus stops to reduce step height, facilitating easy boarding for elderly passengers, strollers, and wheelchair users
2. It locks all four wheels for parking
3. It lowers the bus into underground parking garages at 50 km/h
4. It tilts the bus backward to dump luggage onto the street