code: @Property(
              domainEvent = ClassNameDomainEvent.class
      )
      @PropertyLayout(typicalLength=ApplicationFeature.TYPICAL_LENGTH_CLS_NAME)
      @MemberOrder(name="Id", sequence = "2.3")
      public String getClassName() {
          return getFeatureId().getClassName();
      }
docs: For packages, will be null. Is in this class (rather than subclasses) so is shown in
  {@link ApplicationPackage#getContents() package contents}.