I don't understand the love for Markdown. I get that it is useful for quick and dirty formatting. But as soon as I want to make a document that can interoperate

I don't understand the love for Markdown. I get that it is useful for quick and dirty formatting. But as soon as I want to make a document that can interoperate with others or has long term use requirements, I reach for XHTML. It is not sexy, but it has a well understood definition. As far as I know, Markdown still has a few different definitions that are not perfectly compatible.