Twitter Bootstrap control-group directive

HTML

<link rel="stylesheet" href="//netdna.bootstrapcdn.com/twitter-bootstrap/2.3.2/css/bootstrap-combined.min.css">
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
<script src="//ajax.googleapis.com/ajax/libs/angularjs/1.0.7/angular.min.js"></script>
<form ng-app="app" name="form" class="form-horizontal" ng-controller="ExampleController">
    <div control-group label="Example">
        <input type="text" id="example" name="example" ng-model="data.example" required />
    </div>
</form>

JavaScript

var app = angular.module("app", []);

app.directive("controlGroupX", function () {
    return {
        template:
        '<div class="control-group" ng-class="{ error: isError }">\
            <label class="control-label" for="{{for}}">{{label}}</label>\
            <div class="controls" ng-transclude></div>\
        </div>',

        replace: true,
        transclude: true,
        require: "^form",

        scope: {
            label: "@" // Gets the string contents of the `label` attribute
        },

        link: function (scope, element, attrs, formController) {
            // The <label> should have a `for` attribute that links it to the input.
            // Get the `id` attribute from the input element
            // and add it to the scope so our template can access it.
            var id = element.find(":input").attr("id");
            scope.for = id;

            // Get the `name` attribute of the input
            var inputName = element.find(":input").attr("name");
            // Build the scope expression that contains the validation status.
            // e.g. "form.example.$invalid"
            var errorExpression = [formController.$name, inputName, "$invalid"].join(".");
            // Watch the parent scope, because current scope is isolated.
            scope.$parent.$watch(errorExpression, function (isError) {
                scope.isError = isError;
            });
        }

    };
});

app.controller("ExampleController", ["$scope", function ($scope) {
    $scope.data = {
        example: ""
    };
}]);