anchor.diff:  alphanum_chars() -> "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".
   digit_chars() -> "0123456789".
   
  -ows() -> list(oneof([$\s, $\t])).
  -alpha() -> oneof(alpha_chars()).
  -alphanum() -> oneof(alphanum_chars()).
  -digit() -> oneof(digit_chars()).
  +ows() -> list(elements([$\s, $\t])).
  +alpha() -> elements(alpha_chars()).
  +alphanum() -> elements(alphanum_chars()).
  +digit() -> elements(digit_chars()).
   
   tchar() ->
   	frequency([
  -		{1, oneof([$!, $#, $$, $%, $&, $', $*, $+, $-, $., $^, $_, $`, $|, $~])},
  -		{99, oneof(alphanum_chars())}
  +		{1, elements([$!, $#, $$, $%, $&, $', $*, $+, $-, $., $^, $_, $`, $|, $~])},
  +		{99, elements(alphanum_chars())}
   	]).
   
   token() ->
  
positive.code: 
  etag() ->
  	?LET({Strength, Tag},
  		{oneof([weak, strong]), list(etagc())},
  		begin
  			TagBin = list_to_binary(Tag),
  			{{Strength, TagBin},
  
negative.code: 	]).
  
  langtag_privateuse() -> oneof([[], [$-, langtag_privateuse_nodash()]]).
  langtag_privateuse_nodash() -> [elements([$x, $X]), small_non_empty_list([$-, vector(1, 8, alphanum())])].
  private_language_tag() -> ?LET(T, langtag_privateuse_nodash(), iolist_to_binary(T)).
  
  language_tag() ->
  