-spec accept_header(AvailableLangs, AcceptHeader) -> Result
                       when
                           AvailableLangs :: [{binary(), [binary()]}],
                           AcceptHeader :: cowmachine_req:context() | binary() | undefined,
                           Result :: {ok, binary()} | {error, nomatch | header}.

-spec accept_list(AvailableLangs, AcceptableLangs) -> Result
                     when
                         AvailableLangs :: [{binary(), [binary()]}],
                         AcceptableLangs :: [binary()],
                         Result :: {ok, binary()} | {error, nomatch}.

-spec parse_header(AcceptHeader) -> Result
                      when
                          AcceptHeader :: cowmachine_req:context() | binary() | undefined,
                          Result :: {ok, [binary()]} | {error, nomatch | header}.