docs: public static void mergeFragment(
              Document fragment, Document composite, IAuthorizationPrincipal ap)
              throws AuthorizationException {
          Element fragmentLayout = fragment.getDocumentElement();
          Element fragmentRoot = (Element) fragmentLayout.getFirstChild();
          Element compositeLayout = composite.getDocumentElement();
          Element compositeRoot = (Element) compositeLayout.getFirstChild();
          mergeChildren(fragmentRoot, compositeRoot, ap, new HashSet());
      }