diy调用板块数据，怎么在当前板块显示class

[loop]
<li><a href="{url}">{title}<span class="xg1 num">{posts}</span></a></li>
[/loop]

<li><a href="{url}">{title}<span class="xg1 num">{posts}</span></a></li>
<li class="xw1 a"><a href="{url}">{title}<span class="xg1 num">{posts}</span></a></li>当前板块显示class
<li><a href="{url}">{title}<span class="xg1 num">{posts}</span></a></li>