This. As far as I'm concerned, CommonMark _is_ the canonical standard for Markdown. Gruber has contributed nothing to Markdown in over 12 years, and has refuse

This. As far as I'm concerned, CommonMark _is_ the canonical standard for Markdown. Gruber has contributed nothing to Markdown in over 12 years, and has refused to participate in anyone else's efforts to improve the spec. That's more than enough justification for a fork, and as far as I'm aware there are no other actively maintained Markdown specifications in existence at the moment, so CommonMark _is_ the standard.