anchor.diff:  
   %% @doc Validate the requested X-Ops-Server-API-Version value and populate base_state,
   %% and reply with it as or reply with error if it's not valid.
  --spec server_api_version(undefined|string()) -> api_version().
  +-spec server_api_version(undefined|string()) -> api_version() | {error| string()}.
   server_api_version(undefined) ->
       ?API_MIN_VER;
   server_api_version(RequestedVersion) ->
  
positive.code:     %% create_in_container returns true to mean "is forbidden to do X"
      case create_in_container(Container, Req, State) of
          {true, UpdatedReq, UpdatedState} -> {false, UpdatedReq, UpdatedState};
          {false, UpdatedReq, UpdatedState} -> {true, UpdatedReq, UpdatedState};
          Error -> Error
      end;
  auth_check({container, Container, Permission}, Req, State) ->
      ContainerId = fetch_container_id(Container, Req, State),
  
negative.code: %% general-purpose solution for this is provided right now.
  -spec multi_auth_check(AuthChecks :: [auth_tuple()],
                         Req :: wm_req(),
                         State :: chef_wm:base_state()) ->
                                {true, wm_req(), chef_wm:base_state()} |
                                {false,
                                 FailingTuple :: auth_tuple(),
                                 wm_req(),
                                 chef_wm:base_state()} |
                                {Error :: term(),
                                 FailingTuple :: auth_tuple(),
                                 wm_req(),
                                 chef_wm:base_state()}.
  multi_auth_check([], Req, State) ->
      %% Nothing left to check, must be OK
      {true, Req, State};
  