John Gruber, creator of markdown, wrong about markdown again. ( https://airsource.co.uk/blog/2014/09/04/markdown-has-been-st... )
As its author, he’s right though. There really shouldn’t be a standard considered Standard Markdown. It muddies the fact that it wasn’t published by its author. Maybe Common Markdown would have been a better name between a few large orgs.
And now we're in an odd position where Github and friends all validate their implementations against the CommonMark suites, but refer to the result as "Markdown" to their users, which makes the work they're doing maintaining that stuff especially thankless.