[idle_zealot]

Eh, XML is a machine-readable generic markup language. Why would you prefer using a less powerful format like markdown in a context like message representation? XML with inline tags seems the perfect fit.

[Gigachad]

Less powerful also means less complex and less exploitable. You can very easily grab a markdown renderer rather than trying to decode a .docx for messages.

Pretty much no messaging apps let you create messages more complex than markdown anyway.

[stickfigure]

From a security perspective, I prefer a widespread commonly used XML parser over your custom parser for markdown extensions.