<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8"> 
        <title>Bootstrap 实例 - 表单帮助文本</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>

        <form role="form">
            <span>帮助文本实例</span>
            <input class="form-control" type="text" placeholder="">
            <span class="help-block">一个较长的帮助文本块,超过一行,
                需要扩展到下一行。本实例中的帮助文本总共有两行。</span>
        </form>

    </body>
</html>