How does github fold text blocks?
look at this issuecomment
Check if this follows dear-github issue 166, which mentions:
collapsible sections are supported:
<details>
<summary>Click to expand</summary>
whatever
</details>
See more in this example.
The key is to wrap the whole contents inside the
<p>
:
<details><summary>stuff with *mark* **down**</summary><p>
## _formatted_ **heading** with [a](link)
---
{{standard 3-backtick code block omitted from here due to escaping issues}}
---
Collapsible until here.
</p></details>