yunucms如何实现每N条新闻用虚线分割

<?php $num = 1;?>
<yunu:list cid="21" limit="8" orderby="sort desc" flag="1">
<li>
    <a href="{$list.url}">
        <img data-original="{$list.pic}" alt="{$list.title}" width="180" height="190" img-Auto="true">
        <span>{$list.title}<if condition="$k % 2 eq 0 ">2</if></span>
    </a>
</li>
<if condition="$num % 4 eq 0"><div class="line"></div></if>
<?php $num++;?>
</yunu:list>