private static @Nullable XmlNSDescriptor getDtdDescriptor(@NotNull XmlFile containingFile) {
    final XmlDocument document = containingFile.getDocument();
    if (document == null) {
      return null;
    }
    final String url = XmlUtil.getDtdUri(document);
    if (url == null) {
      return null;
    }
    return document.getDefaultNSDescriptor(url, true);
  }
private static @Nullable XmlNSDescriptor getDtdDescriptor(@NotNull XmlFile containingFile)