@Override
  public void indexStub(@NotNull ElementStub stub, @NotNull IndexSink sink) {
    final String namespaceKey = stub.getNamespaceKey();
    if (StringUtil.isNotEmpty(namespaceKey)) {
      sink.occurrence(DomNamespaceKeyIndex.KEY, namespaceKey);
    }

    final String elementClass = stub.getElementClass();
    if (elementClass != null) {
      sink.occurrence(DomElementClassIndex.KEY, elementClass);
    }
  }
@Override
  public void indexStub(@NotNull ElementStub stub, @NotNull IndexSink sink)