anchor.diff:  
   etag() ->
   	?LET({Strength, Tag},
  -		{oneof([weak, strong]), list(etagc())},
  +		{elements([weak, strong]), list(etagc())},
   		begin
   			TagBin = list_to_binary(Tag),
   			{{Strength, TagBin},
  
positive.code: alphanum_chars() -> "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".
  digit_chars() -> "0123456789".
  
  ows() -> list(oneof([$\s, $\t])).
  alpha() -> oneof(alpha_chars()).
  alphanum() -> oneof(alphanum_chars()).
  digit() -> oneof(digit_chars()).
  
  tchar() ->
  	frequency([
  		{1, oneof([$!, $#, $$, $%, $&, $', $*, $+, $-, $., $^, $_, $`, $|, $~])},
  		{99, oneof(alphanum_chars())}
  	]).
  
  token() ->
  
negative.code: expect() ->
  	?LET(E,
  		[$1, $0, $0, $-,
  			elements([$c, $C]), elements([$o, $O]), elements([$n, $N]),
  			elements([$t, $T]), elements([$i, $I]), elements([$n, $N]),
  			elements([$u, $U]), elements([$e, $E])],
  		list_to_binary(E)).
  
  prop_parse_expect() ->
  