This Clause defines ReferenceTypes that are needed beyond those already specified as part of 10000-3 and 10000-5. This includes extending TwoStateVariableType state machines with sub states and the addition of Alarm grouping. TwoStateVariableTypes can be extended with subordinate state machines in a similar fashion to the StateMachineType defined in 10000-16.

The TwoStateVariableType References will only exist when sub states are available. For example, if a TwoStateVariableType machine is in a False State, then any sub states referenced from the True state will not be available and will be reported as a NULL.