anchor.diff:  		<<"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.
  
positive.code: -export([parse_accept_encoding/1]).
  -export([parse_accept_language/1]).
  -export([parse_age/1]).
  -export([parse_cache_control/1]).
  -export([parse_connection/1]).
  -export([parse_content_encoding/1]).
  
negative.code: %% Only return if the list is not empty.
  nonempty(L) when L =/= [] -> L.
  
  %% Parse a list of case sensitive tokens.
  token_list(<<>>, Acc) -> lists:reverse(Acc);
  token_list(<< $\s, R/bits >>, Acc) -> token_list(R, Acc);
  token_list(<< $\t, R/bits >>, Acc) -> token_list(R, Acc);
  token_list(<< $,, R/bits >>, Acc) -> token_list(R, Acc);
  token_list(<< C, R/bits >>, Acc) when ?IS_TOKEN(C) -> token(R, Acc, << C >>).
  
  token(<<>>, Acc, T) -> lists:reverse([T|Acc]);
  token(<< $\s, R/bits >>, Acc, T) -> token_list_sep(R, [T|Acc]);
  token(<< $\t, R/bits >>, Acc, T) -> token_list_sep(R, [T|Acc]);
  token(<< $,, R/bits >>, Acc, T) -> token_list(R, [T|Acc]);
  token(<< C, R/bits >>, Acc, T) when ?IS_TOKEN(C) -> token(R, Acc, << T/binary, C >>).
  
  token_list_sep(<<>>, Acc) -> lists:reverse(Acc);
  token_list_sep(<< $\s, R/bits >>, Acc) -> token_list_sep(R, Acc);
  token_list_sep(<< $\t, R/bits >>, Acc) -> token_list_sep(R, Acc);
  token_list_sep(<< $,, R/bits >>, Acc) -> token_list(R, Acc).
  
  %% 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);
  