1、实现Bootstrap导航条鼠标悬停显示下拉菜单（bootstrap默认的是点击触发）
一般的导航例子如下：
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Bootstrap导航条鼠标悬停下拉菜单</title>
<link id="bootstrap_221" rel="stylesheet" type="text/css" class="library" href="/js/sandbox/bootstrap-2.2.1/css/bootstrap.min.css">
<script id="jquery_172" type="text/javascript" class="library" src="/js/sandbox/jquery/jquery-1.7.2.min.js"></script>
<script id="bootstrap_221" type="text/javascript" class="library" src="/js/sandbox/bootstrap-2.2.1/js/bootstrap.min.js"></script>
</head>
<body>
<div class="container">
<div class="span12">
<h1>Bootstrap导航条鼠标悬停下拉菜单</h1>
<p>Bootstrap的导航条下拉菜单为了适应移动设备没有鼠标hover的状态，都是点击弹出下拉菜单，为了适应一般网站使用，我稍作了一些修改，鼠标hover时就弹出二级菜单。</p>
<div class="navbar">
<div class="navbar-inner">
<ul class="nav">
<li><a href="#">Menu1</a></li>
<li><a href="#">Menu2</a></li>
<li class="dropdown"> <a href="#menu3" class="dropdown-toggle" data-toggle="dropdown">Menu3</a>
<ul class="dropdown-menu">
<li><a href="#menu7">Menu7</a></li>
<li><a href="#menu8">Menu8</a></li>
</ul>
</li>
</ul>
</div>
</div>
</div>
</div>
</body>
</html>
改变后的代码如下（去掉上面黄色代码部分，增加下面绿色代码样式）：
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Bootstrap导航条鼠标悬停下拉菜单</title>
<link id="bootstrap_221" rel="stylesheet" type="text/css" class="library" href="/js/sandbox/bootstrap-2.2.1/css/bootstrap.min.css">
<script id="jquery_172" type="text/javascript" class="library" src="/js/sandbox/jquery/jquery-1.7.2.min.js"></script>
<script id="bootstrap_221" type="text/javascript" class="library" src="/js/sandbox/bootstrap-2.2.1/js/bootstrap.min.js"></script>
<style>
.navbar .nav > li:hover .dropdown-menu {display: block;}
</style>
</head>
<body>
<div class="container">
<div class="span12">
<h1>Bootstrap导航条鼠标悬停下拉菜单</h1>
<p>Bootstrap的导航条下拉菜单为了适应移动设备没有鼠标hover的状态，都是点击弹出下拉菜单，为了适应一般网站使用，我稍作了一些修改，鼠标hover时就弹出二级菜单。</p>
<div class="navbar">
<div class="navbar-inner">
<ul class="nav">
<li><a href="#">Menu1</a></li>
<li><a href="#">Menu2</a></li>
<li class="dropdown"> <a href="#menu3">Menu3</a>
<ul class="dropdown-menu">
<li><a href="#menu7">Menu7</a></li>
<li><a href="#menu8">Menu8</a></li>
</ul>
</li>
</ul>
</div>
</div>
</div>
</div>
</body>
</html>