When may a driver leave their seat and leave the vehicle?
Explanation
When leaving the vehicle, the driver must take every necessary step to keep it stable and safe. That is not a single action but a whole set of them: engage the parking brake, leave it in gear, turn the wheels, and lock the car.
KET reference: KET 147: A driver may leave their seat or the vehicle only after ensuring it will not roll away on its own and others cannot use it.