code: public B message(String messageName) {
      MessageEventDefinition messageEventDefinition = createMessageEventDefinition(messageName);
      element.getEventDefinitions().add(messageEventDefinition);
  
      return myself;
    }
docs: Sets an event definition for the given message name. If already a message
  with this name exists it will be used, otherwise a new message is created.
  
  @param messageName the name of the message
  @return the builder object