通過一個執行個體代碼來說明：
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>CSS-expression Example</title>
<style>
tr
{
background-color:expression(
(this.sectionRowIndex%2!=0)?"white":"#e8e8e8"
);
mevent:expression( //這裡的mevent是自訂的屬性名稱
onmouseover=function(){
this.style.backgroundColor="#0099cc";
},
onmouseout=function(){
this.style.backgroundColor="";
}
)
}
</style>
</head>
<body >
<table name="tab" id="tab" width="100%" border="1" cellspacing="0" cellpadding="0">
<tr>
<td> </td>
<td> </td>
<td> </td>
<td> </td>
</tr>
<tr >
<td> </td>
<td> </td>
<td> </td>
<td> </td>
</tr>
<tr >
<td> </td>
<td> </td>
<td> </td>
<td> </td>
</tr>
<tr >
<td> </td>
<td> </td>
<td> </td>
<td> </td>
</tr>
</table>
</body>
</html>
可以看出CSS的expression功能的兩個優點：
1.可以對HTML對象進行批量處理，大大地簡化了寫JS代碼的工作。
2.使CSS和HTML代碼有效地分離，使CSS代碼和HTML元素的耦合度減小，便於代碼的維護。
其實expression就是把JS代碼內嵌到了CSS屬性中
但是這種用法也有一個缺點，就是特別消耗資源，要嚴格控制這種方法的用量。不然頁面會變得非常慢。
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