表单控件中元素input的属性novalidate的操作实例是什么呢？

<button id="btn1">打开验证</button>
<button id="btn2">关闭验证</button>
<form method="get" action="#" name="test">
    E-mail: <input type="email" name="user_email" />
    <input type="submit" />
</form>    
<script>
var oForm = document.forms.test;
btn1.onclick = function(){
    oForm.removeAttribute('novalidate');
};
btn2.onclick = function(){
    oForm.setAttribute('novalidate','');
};
</script>