Texmacs could be that thing, depending on your definition of "text-based": https://www.texmacs.org/tmweb/manual/webman-format.en.html https://www.texmacs.org/tm

Texmacs could be that thing, depending on your definition of "text-based": https://www.texmacs.org/tmweb/manual/webman-format.en.html https://www.texmacs.org/tmweb/manual/webman-format.en.html