The HTML Details Element (<details>) creates a disclosure widget in which information is visible only when the widget is toggled into an "open" state. A summary or label can be provided using the <summary> element. https://developer.mozilla.org/en-US/docs/Web/HTML/Element/details.
This is a feature I enjoy in Github, see this informative and succinct post about using this feature when writing GitHub Flavored Markdown (GFM): Using <details> <summary> expandable content on GitHub with Markdown
I would like to be able to use this or a similar feature while authoring nodebb posts.