Plain text is handy.
Discussion
because you can easily search trough it. A search bar is the most important. Not on the server, but just local. In the browser or text editor.
This would be my top documentation experience:
I have a problem, I visit documentation site, I see everything in plain text and thus I can search in an instant trough all text to find what I need. I might even easily copy all text at once, paste it into vim or another text editor, and use advanced search. I could even use `git grep "search string"` if the documentation is a github repo.