code: function _Overlay_verifyCommandsOnly(element, type) {
                      var children = element.children;
                      var commands = new Array(children.length);
                      for (var i = 0; i < children.length; i++) {
                          // If constructed they have win-command class, otherwise they have data-win-control
                          if (!_ElementUtilities.hasClass(children[i], "win-command") &&
                          children[i].getAttribute("data-win-control") !== type) {
                              // Wasn't tagged with class or AppBar/MenuCommand, not an AppBar/MenuCommand
                              throw new _ErrorFromName("WinJS.UI._Overlay.MustContainCommands", strings.mustContainCommands);
                          } else {
                              // Instantiate the commands.
                              ControlProcessor.processAll(children[i]);
                              commands[i] = children[i].winControl;
                          }
                      }
                      return commands;
                  }
docs: Verify that this HTML AppBar only has AppBar/MenuCommands.