What is the purpose of the dust seal (wiper seal) located on the outer edge of a disc brake caliper piston?

1. To prevent dirt, water, and debris from entering the caliper bore and damaging the pressure seal
2. To keep high-pressure brake fluid from leaking out of the caliper
3. To push the brake pads back away from the rotor when the brake is released
4. To indicate to the technician when the brake pads are worn out