@Override
  protected void addCompletions(@NotNull CompletionParameters parameters,
                                @NotNull ProcessingContext context,
                                @NotNull CompletionResultSet result) {
    PsiReference reference = parameters.getPosition().getContainingFile().findReferenceAt(parameters.getOffset());
    if (reference instanceof XmlAttributeReference) {
      addAttributeReferenceCompletionVariants((XmlAttributeReference)reference, result, null);
    }
  }
@Override
  protected void addCompletions(@NotNull CompletionParameters parameters,
                                @NotNull ProcessingContext context,
                                @NotNull CompletionResultSet result)