> Why and how to preserve digital content in plaintext format for long-term accessibility and reuse

The author actually doesn't think Markdown is the only correct storage format. All lightweight markup languages will do. They just use Markdown themselves. It's good they allow Mycomarkup, I'd've written a remarque here otherwise. 

I myself am not sure if it's the right way. Maybe the websites should be preserved closer to the way they were made? I'll now archive this page, in HTML.