A completion transition is a transition originating from a state or an exit point, and does not have an explicit trigger, although it may have a guard defined. For a simple state, if it is active at the beginning of simulation step, then its completion transition may be executed.
If the state is a composite state or a submachine state, a completion transition may be executed if either the submachine or the composite state is active at the beginning of simulation step, and its contained regions have reached final states. If multiple completion transitions are defined for a state, then they should have mutually exclusive guard conditions.