anchor.diff:  -export([parse_accept_encoding/1]).
   -export([parse_accept_language/1]).
   -export([parse_age/1]).
  +-export([parse_allow/1]).
   -export([parse_cache_control/1]).
   -export([parse_connection/1]).
   -export([parse_content_encoding/1]).
  
positive.code: %% Only return if the list is not empty.
  nonempty(L) when L =/= [] -> L.
  
  %% Parse a list of case insensitive tokens.
  token_ci_list(<<>>, Acc) -> lists:reverse(Acc);
  token_ci_list(<< $\s, R/bits >>, Acc) -> token_ci_list(R, Acc);
  
negative.code: 		<<"4.17">>
  	],
  	[{V, fun() -> {'EXIT', _} = (catch parse_age(V)) end} || V <- Tests].
  -endif.
  
  %% @doc Parse the Allow header.
  
  -spec parse_allow(binary()) -> [binary()].
  parse_allow(Allow) ->
  	token_list(Allow, []).
  
  -ifdef(TEST).
  allow() ->
  	?LET(L,
  		list({ows(), ows(), token()}),
  		case L of
  			[] -> {[], <<>>};
  			_ ->
  				<< _, Allow/binary >> = iolist_to_binary([[OWS1, $,, OWS2, M] || {OWS1, OWS2, M} <- L]),
  				{[M || {_, _, M} <- L], Allow}
  		end).
  
  prop_parse_allow() ->
  	?FORALL({L, Allow},
  		allow(),
  		L =:= parse_allow(Allow)).
  
  parse_allow_test_() ->
  	Tests = [
  		{<<>>, []},
  		{<<"GET, HEAD, PUT">>, [<<"GET">>, <<"HEAD">>, <<"PUT">>]}
  	],
  	[{V, fun() -> R = parse_allow(V) end} || {V, R} <- Tests].
  -endif.
  
  -ifdef(PERF).
  horse_parse_allow() ->
  	horse:repeat(200000,
  		parse_allow(<<"GET, HEAD, PUT">>)
  	).
  -endif.
  
  %% @doc Parse the Cache-Control header.
  