anchor.diff:  
   %% @doc Default values for semantic header parsing.
   -spec parse_header_default(binary()) -> any().
  -parse_header_default(<<"connection">>) -> [];
   parse_header_default(<<"transfer-encoding">>) -> [<<"identity">>];
   parse_header_default(_Name) -> undefined.
   
  
positive.code: 			cowboy_http:nonempty_list(Value, fun cowboy_http:language_range/2)
  		end);
  parse_header(Name, Req, Default) when Name =:= <<"content-length">> ->
  	parse_header(Name, Req, Default,
  		fun (Value) ->
  			cowboy_http:digits(Value)
  		end);
  parse_header(Name, Req, Default) when Name =:= <<"content-type">> ->
  	parse_header(Name, Req, Default,
  		fun (Value) ->
  			cowboy_http:content_type(Value)
  		end);
  parse_header(Name, Req, Default) when Name =:= <<"expect">> ->
  	parse_header(Name, Req, Default,
  		fun (Value) ->
  
negative.code: 		end);
  parse_header(Name, Req, Default)
  		when Name =:= <<"if-match">>; Name =:= <<"if-none-match">> ->
  	parse_header(Name, Req, Default, fun cowboy_http:entity_tag_match/1);
  parse_header(Name, Req, Default)
  		when Name =:= <<"if-modified-since">>;
  			Name =:= <<"if-unmodified-since">> ->
  	parse_header(Name, Req, Default, fun cowboy_http:http_date/1);
  %% @todo Extension parameters.
  parse_header(Name, Req, Default) when Name =:= <<"transfer-encoding">> ->
  	parse_header(Name, Req, Default,
  