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    <head>
        <meta charset="utf-8"> 
        <title>Bootstrap 实例 - 插入符</title>
        <link rel="stylesheet" href="https://cdn.staticfile.org/twitter-bootstrap/3.3.7/css/bootstrap.min.css">  
        <script src="https://cdn.staticfile.org/jquery/2.1.1/jquery.min.js"></script>
        <script src="https://cdn.staticfile.org/twitter-bootstrap/3.3.7/js/bootstrap.min.js"></script>
    </head>
    <body>

        <p>插入符实例
            <span class="caret"></span>
        </p>

    </body>
</html>