What is Markdown?

Plain text with just enough punctuation to imply formatting, which is why it ended up as the default for READMEs, issues, wikis and notes. Its tables are the awkward part - a pipe-and-dash grid that's readable enough written by hand and tedious to maintain by hand.

What is XML?

Verbose, strict, and still holding up enormous amounts of the world - government feeds, financial messaging, publishing, office documents. JSON took the web from it, but anywhere with schemas and validators and twenty years of history, XML is what's on the wire.