anchor.diff:  
   %% @doc Return true if the given character is a private use character
   %% as defined by https://tools.ietf.org/html/rfc3454#appendix-C.3
  +-spec is_private_use_characters(char()) -> boolean().
   is_private_use_characters(C) ->
       (16#E000 =< C andalso C =< 16#F8FF)
            orelse (16#F000 =< C andalso C =< 16#FFFFD)
  
positive.code: 
  %% @doc Return true if the given character is a non-character code point
  %% as defined by https://tools.ietf.org/html/rfc3454#appendix-C.4
  is_non_character_code_points(C) ->
      (16#FDD0 =< C andalso C =< 16#FDEF)
          orelse (16#FFFE =< C andalso C =< 16#FFFF)
  
negative.code: 
  %% @doc Return true if the given character is a tagging character as defined by
  %% https://tools.ietf.org/html/rfc3454#appendix-C.9
  -spec is_tagging_char(char()) -> boolean().
  is_tagging_char(C) ->
      C == 16#E0001 orelse
          (16#E0020 =< C andalso C =< 16#E007F).
  