我想问下theme/inc 下about.php文件中的这些变量<div class="desc">{$index.about_content|truncate:180:"..."}</div> <h1>{$site.site_name}</h1>是在哪里调用

<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<div class="about">
<h1>{$site.site_name}</h1>
<div class="desc">{$index.about_content|truncate:180:"..."}</div>
<a href="{$index.about_link}" class="more">{$lang.about_link}</a>
</div>