Sub-scenarios and actors

What happens if a scenario that contains unconstrained actors is invoked by another scenario? How is the actor created?

scenario my_scenario:
    my_car: vehicle
    do my_car.drive()

scenario main:
    main_car: vehicle
    other_car: vehicle
    do serial:
        main_car.drive()
        my_scenario()

I can see multiple possibilities:

• my_car is created when the main scenario starts, but has no directions until my_scenario is executed
• my_car is created dynamically as a new vehicle during execution, when my_scenario starts and vanishes when that sub-scenario has finished
• one of the existing main scenario vehicles is chosen at random
• an error is raised, because the scenario is using a car that doesn't exist