[tkainrad]

I think Markdown does qualify as machine-readable. There are very good libraries to do all kinds of things with it.

Edit: I guess you meant human-readable as opposed to things like base64, and not as a critique against Markdown.

By now, there are several unofficial APIs at least, for read-access they are quite good apparently, did not yet use one myself though. E.g. https://github.com/kjk/notionapi