anchor.diff:  %% Add protocol if it doesn't exist
   -spec normalize_url(Url) -> binary() when
       Url :: binary().
  +normalize_url(Url) when Url =:= undefined ->
  +    <<"">>;
   normalize_url(Url) when is_list(Url) ->
       normalize_url(list_to_binary(Url));
   normalize_url(<<"http://", T/binary>>) ->
  
positive.code: fetch(Url0, Options, Rules) ->
      Url = normalize_url(Url0),
      UrlContext = url_context(Url),
      case get_page_body(Url) of
          {Length, Body} when is_integer(Length) ->
              Fetched = parse_body(Body, Rules, Options),
              [
  
negative.code:         Error -> Error
      end.
  
  -spec remove_duplicates(L) -> list() when
      L :: list().
  remove_duplicates(L) ->
  