iframe 元素会创建包含另外一个文档的内联框架（即行内框架）。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>内联框架</title>
</head>
<body>
<center>
<h1>欢迎使用QQ邮箱</h1>
<iframe width="300px" src="zuo.html" name="wind1"></iframe>
<iframe width="500px" src="" name="wind2"></iframe>
</center>
</body>
</html>
zuo.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>zuo</title>
</head>
<body>
<center>
<a href="sjx.html" target="wind2">收件箱</a><br>
<a href="fjx.html" target="wind2">发件箱</a><br>
<a href="cgx.html" target="wind2">草稿箱</a>
</center>
</body>
</html>
sjx.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>收件箱</title>
</head>
<body>
<h2>1、小明生日提醒</h2>
<h2>2、小明婚礼邀请</h2>
</body>
</html>