There is CommonMark, but even that is very opiniated. One of the issues is that original Markdown used tabs everywhere, but people started using spaces, but so

There is CommonMark, but even that is very opiniated. One of the issues is that original Markdown used tabs everywhere, but people started using spaces, but some implementations choke down on them. The biggest issue in Markdown is that whitespace is significant and important; and there are tons of weird edgecases of all the various rules clashing with each other. Even CommonMark has some weird unspecified edgecases. I was briefly involved with a Markdown parser implementation… it’s really really hard to parse MarkDown. Not sure if harder than to parse HTML, as I did not do that. But it’s still really really hard.