样式表达式实现交替显示table行颜色

<heand> 
<mce:style type="text/css"><!-- 
tr {background-color:expression((this.sectionRowIndex%2==0)?"#419C33":"#CCEBC7")} 
--></mce:style><style type="text/css" mce_bogus="1">tr {background-color:expression((this.sectionRowIndex%2==0)?"#419C33":"#CCEBC7")}</style> 
<mce:style type="text/css"><!-- 
tr.lightrow td { 
background-color: #FFFFFF; 
} 
tr.darkrow td { 
background-color: #EFEFEF; 
} 
--></mce:style><style type="text/css" mce_bogus="1">tr.lightrow td { 
background-color: #FFFFFF; 
} 
tr.darkrow td { 
background-color: #EFEFEF; 
}</style> 
<table id="main_table"> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
<tr> 
<td width="100">a</td> 
<td width="100">b</td> 
</tr> 
</table>