A Pico CMS simply plugin for render subtemplate to main layout.
In default Pico, you can change only main template by setting Template meta.
This plugin allows you to setup something like nested template.
Create custom named template in you Theme dir e.g. sidebar.html
<div class="sub-content">
{{ content }}
</div>
<div class="sidebar">
<ul>
<li>Feature 1</li>
<li>Feature 2</li>
</ul>
</div>In your .md file add meta Subtemplate: sidebar
That's all