...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Interrupt states: a terminate state which can be exited if a defined event is triggered.
Kleene (any) event: a transition with a kleene event will accept any event as trigger. Unlike a completion transition, an event must be triggered and the original event is kept accessible in the kleene event.