code: @Deprecated
      public Collection<SimpleElement> getAdditionalElements() {
          return getExtensionElements()
              .stream()
              .filter(e -> e instanceof SimpleElement)
              .map(SimpleElement.class::cast)
              .collect(Collectors.toList());
      }
docs: @return a filtered {@link Collection} of {@link SimpleElement}
  
  @deprecated will be removed in next version. Use {@link #getExtensionElements} instead.