code: public SignalEventDefinitionBuilder signalEventDefinition(String signalName) {
      SignalEventDefinition signalEventDefinition = createSignalEventDefinition(signalName);
      element.getEventDefinitions().add(signalEventDefinition);
  
      return new SignalEventDefinitionBuilder(modelInstance, signalEventDefinition);
    }
docs: Sets an event definition for the given Signal name. If a signal with this
  name already exists it will be used, otherwise a new signal is created.
  It returns a builder for the Signal Event Definition.
  
  @param signalName the name of the signal
  @return the signal event definition builder object