anchor.diff:          '__mandatory' => [key()],                   % Mandatory fields for this level
           '__unique_keys' => [key()],                 % Checks that keys are unique in a list
           '__allow_unknown' => boolean(),             % Allow unknown fields
  +        '__skip_invalid' => boolean(),
           '__post_check' => post_check_fun()
       }.
   
  
positive.code:     syntax :: map(),
      path :: binary(),
      allow_unknown :: boolean(),
      opts :: parse_opts()
  }).
  
  
negative.code:         _ ->
              maps:get(allow_unknown, Opts, false)
      end,
      SkipInvalid = case Syntax of
          #{'__skip_invalid':=Skip} ->
              Skip;
          _ ->
              maps:get(skip_invalid, Opts, false)
      end,
      Parse = #parse{
          syntax = Syntax,
          opts = Opts,
          path = maps:get(path, Opts, <<>>),
          allow_unknown = AllowUnknown,
          skip_invalid = SkipInvalid
      },
      case do_parse(Terms, Parse) of
          {ok, #parse{ok=Ok, no_ok=NoOk}} ->
  