With respect to your question: "I don't really understand the version number means in this case?" An item can be booted only if its version number has not regr

With respect to your question: "I don't really understand the version number means in this case?" An item can be booted only if its version number has not regressed in to prevent replay attacks. There are no cancellation ids in the Actor implementation, however a cancellation exception can be thrown when an activity is cancelled.