<head>
</head>
<!--
Inline var could be used:
- {level} - the heading level (from html)
- {title}    - title of the section, MUST BE OCCURED EXACTLY ONCE
- {content} - content of the current section, MUST BE OCCURED EXACTLY ONCE
- {numbering} - heading-numbering of the section
- Any meta contents.
-->
<body>
  <section class="block">
    <details open>
      <summary style="font-size: 117%;">{numbering} {title}</summary>
      {content}
    </details>
  </section>
  <!-- you can do this: <h{level}>{content}