public static void copyMissingContent(@NotNull Element source, @NotNull Element target) {
    Element targetClone = target.clone();
    for (Attribute attribute : source.getAttributes()) {
      if (!hasAttribute(targetClone, attribute.getName())) {
        target.setAttribute(attribute.clone());
      }
    }
    for (Content content : source.getContent()) {
      if (!hasContent(targetClone, content)) {
        target.addContent(content.clone());
      }
    }
  }
public static void copyMissingContent(@NotNull Element source, @NotNull Element target)