angularjs – ngModel $modelValue和ngModel之间有什么区别$view

app.directive('ckEditor',[function () {
    return {
        require: '?ngModel',link: function ($scope,elm,attr,ngModel) {

            var ck = null;
            var config = attr.editorSize;
            if (config == 'wide') {
                ck = CKEDITOR.replace(elm[0],{ customConfig: 'config-wide.js' });
            } else {
                ck = CKEDITOR.replace(elm[0],{ customConfig: 'config-narrow.js' });
            }


            function updateModel() {
                $scope.$apply(function () {
                    ngModel.$setViewValue(ck.getData());
                });
            }

            $scope.$on('modalObjectSet',function (e,modalData) {
                // force a call to render
                ngModel.$render();
            });

            ck.on('change',updateModel);
            ck.on('mode',updateModel);
            ck.on('key',updateModel);
            ck.on('dataReady',updateModel);

            ck.on('instanceReady',function () {
                ngModel.$render();
            });

            ck.on('insertElement',function () {
                setTimeout(function () {
                    $scope.$apply(function () {
                        ngModel.$setViewValue(ck.getData());
                    });
                },1000);
            });

            ngModel.$render = function (value) {
                ck.setData(ngModel.$modelValue);
            };

            ngModel.$render = function (value) {
                ck.setData(ngModel.$viewValue);
            };
        }
    };
}])

有人可以告诉我有什么区别：

ck.setData(ngModel.$modelValue);
ck.setData(ngModel.$viewValue);

和我应该使用。我看了角度文档，它说：

$viewValue

Actual string value in the view.

$modelValue

The value in the model,that the control is bound to.

我不知道作者的意思，当他在文档中写这个:-(