@Nullable
  public static Grammar getGrammar(@NotNull XmlFile element) {
    if (element instanceof RncFile) {
      return ((RncFile)element).getGrammar();
    }
    final DomFileElement<RngGrammar> fileElement = DomManager.getDomManager(element.getProject()).getFileElement(element, RngGrammar.class);
    return fileElement != null ? fileElement.getRootElement() : null;
  }
@Nullable
  public static Grammar getGrammar(@NotNull XmlFile element)