表单控件位于<form>元素中。每个<form>元素都应该设置action特性，通常还要设置method特性和id特性
<!DOCTYPE html>
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<html>
<head>
<title>TODO supply a title</title>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body>
<div>TODO write content</div>
<form action="http://www.example.com/subscribe.php" method="get">
<p>其特性值是服务器上一个页面的URL，这个页面用来在用户提交表单时接受表单中的信息。</p>
</form>
</body>
</html>