ite necessary `NgModelController` methods&#10;      ctrl.$isEmpty = isEmpty;&#10;      ctrl.$render = render;&#10;&#10;      // Bind to events&#10;      elem.on(&#39;click&#39;, function(event) {&#10;        event.preventDefault();&#10;        scope.$apply(toggleCheckbox);&#10;      });&#10;      elem.on(&#39;keypress&#39;, function(event) {&#10;        event.preventDefault();&#10;        if (event.keyCode === 32 || event.keyCode === 13) {&#10;          scope.$apply(toggleCheckbox);&#10;        }&#10;      