Car engineers know what level 1-5 is. Level 1 and 2 are basic assist - cruise control and the like. Level 3 is the car drives but the driver monitors everything for issues the car can't detect. 4 and 5 are you can go to sleep, 4 means there are some situations the car will wake you up and after you get a coffee (ie there is no need for instant take over) you drive, while 5 is the car will drive anything.