anchor.diff:      "a" = first_char("aap"),
       "Ж" = first_char("ЖЖЖxx"),
       "ć" = first_char("ćaap"),
  +
  +    <<"abcdef">> = concat(<<"abc">>, <<"def">>),
  +    <<"abcdef">> = concat(<<"abc">>, "def"),
  +    "abcdef" = concat("abc", "def"),
  +    "abcdef" = concat("abc", <<"def">>),
  +    "abcdef" = concat("abc", def),
  +    
       ok.
  
positive.code: split_prefix(_,     _)     -> no.
  
  
  test() ->
      A = "üçgen",
      A = to_lower(to_upper(A)),
  
negative.code: 
  %% interface functions
  -export([
           trim/1,
           trim_left/1,
           trim_right/1,
           trim/2,
           trim_left/2,
           trim_right/2,
           trim_left_func/2,
           is_string/1,
           first_char/1,
           last_char/1,
           unquote/1,
           unquote/2,
           nospaces/1,
           line/1,
           to_rootname/1,
           to_name/1,
           to_slug/1,
           to_lower/1,
           to_upper/1,
           replace/3,
           sanitize_utf8/1,
           truncate/2,
           truncate/3,
           truncatewords/2,
           truncatewords/3,
           split_lines/1,
           escape_ical/1,
           starts_with/2,
           ends_with/2,
           contains/2,
           split/2,
           concat/2,
           test/0
          ]).
  
  
  %% @doc Remove whitespace at the start and end of the string
  