code: public StateConfiguration<S, T> substateOf(S superstate) {
          StateRepresentation<S, T> superRepresentation = lookup.call(superstate);
          representation.setSuperstate(superRepresentation);
          superRepresentation.addSubstate(representation);
          return this;
      }
docs: Sets the superstate that the configured state is a substate of
  <p>
  Substates inherit the allowed transitions of their superstate.
  When entering directly into a substate from outside of the superstate,
  entry actions for the superstate are executed.
  Likewise when leaving from the substate to outside the supserstate,
  exit actions for the superstate will execute.
  
  @param superstate The superstate
  @return The receiver