In search of a non-electron text editor that can fold | Are emacs and (neo)vim my only options?
(discuss.online)
The following gif demonstrates folding:
SublimeText seems to have it. I don’t personally use it but it’s a pretty competent editor and it’s not in the feature table from the Wikipedia page someone else shared.
Sublime 3 was limited to folding by indentation; I’m not sure if that’s true for Sublime 4 as well, but the Markdown plugin docs have a note on folding and mention you can fold by section and heading levels.