为什么不录入内容，边框红色的提示样式也出不来呢？
var S14Module = angular.module("S14Module", []);
S14Module.controller("S14Ctrl", ["$scope", function($scope){
$scope.user={
username: 'abc',
password: ''
};
$scope.save=function(){
alert("Save data!");
}
}]);<!DOCTYPE html>
<html ng-app="S14Module">
<head>
<meta charset="utf-8">
<title>Angular event</title>
<!-- <link rel="stylesheet" type="text/css" href="bootstrap.min.css"> -->
<script src="angular.min.js"></script>
<script src="myjs/study14.js"></script>
</head>
<body>
<form name="myform" ng-submit="save()" ng-controller="S14Ctrl">
<input name="username" type="text" ng-model="user.username" required>
<input name="password" type="password" ng-model="user.password" required>
<input type="submit" ng-disabled="myform.$invalid"/>
</form>
</body>
</html>
