Hugo uses Markdown for its simple content format. However, there are a lot of things that Markdown doesn’t support well. You could use pure HTML to expand possibilities.
But this happens to be a bad idea. Everyone uses Markdown because it’s pure and simple to read even non-rendered. You should avoid HTML to keep it as simple as possible.
To avoid this limitations, Hugo created shortcodes. A shortcode is a simple snippet inside a page.
The Relearn theme provides multiple shortcodes on top of existing ones.
The Attachments shortcode displays a list of files attached to a page
Nice buttons on your page
List the child pages of a page
Displays an expandable/collapsible section of text on your page
Displays content from other Markdown files
Generation of diagram and flowchart from text in a similar manner as Markdown
Disclaimers to help you structure your page
Get value of site params variables in your page
Synchronize selection of content in different tabbed views