阻止CKEditor删除在源代码模式下分配的类？

CKEDITOR.on('instanceReady', function (event) {
    event.editor.dataProcessor.htmlFilter.addRules({
        elements: {
            $: function (element) {
                // 阻止删除class属性
                element.attributes['class'] = element.attributes['class'] || '';
                return element;
            }
        }
    });
});

CKEDITOR.replace('editor', {
    on: {
        instanceReady: function (event) {
            event.editor.dataProcessor.htmlFilter.addRules({
                elements: {
                    $: function (element) {
                        // 阻止删除class属性
                        element.attributes['class'] = element.attributes['class'] || '';
                        return element;
                    }
                }
            });
        }
    }
});