UMLR — Priority of the joint transition

The specification says that: "The priority of joined transitions is based on the priority of the transition with the most transitively nested source state". Suppose that a join transition is has two transitions with source states at the same depth, but in two different regions. How is is established which of the two transition defines the priority of the join transition?. Notice that, depending on which transition is choosen, different other transitions might be allowed or disallowed to be fired. Some possible anwers are: - Any of the two transitions can be chosen statically. (i.e. the priority of the join transition always remains the same). - Any of the two transitions can be chosen, and the choice truly, completely nondeterministic (hence possibly dynamic) I.e. the priority of the join transitions can change each time the join transition is fired.