XML has its strengths as a markdown format. My own formatted text format ETML is based on XML, as I could recycle old HTML conventions (still has stylesheet as an option), and I can store multiple text blocks in an XML file. It's not something my main choice of human readable format SDL excels at, which itself has its own issues (I'm writing my own extensions/refinements for it by the name XDL, with hexadecimal numbers, ISO dates, etc.).