anchor.diff:                       {ok, Parse4};
                    {error, unknown} ->
                        error({invalid_syntax, SyntaxOp});
  +                 {error, syntax} when SkipInvalid ->
  +                     {ok, Parse};
                    {error, syntax} ->
                        {error, syntax_error(Key2, Parse)};
                    {error, Error} ->
  
positive.code: 
  
  %% @private
  do_parse_key(Key, Val, #parse{allow_unknown=AllowUnknown}=Parse) ->
       case find_syntax(Key, Parse) of
           {ok, _Key2, ignore} ->
               {ok, Parse};
  
negative.code:     syntax :: map(),
      path :: binary(),
      allow_unknown :: boolean(),
      skip_invalid :: boolean(),
      opts :: parse_opts()
  }).
  
  