<details> tag creates a widget whose content becomes visible or invisible by the user toggling its visibility (typically by clicking a triangle). <!doctype html>
<html><body>
The three main <a href='development/languages/Metasyntactic-variables'>metasyntactic variables</a>:
<details>
<ul style='margin-top:0'>
<li>foo
<li>bar
<li>baz
</ul>
</details>
More text …
</body></html>
<details> content: