[microtonal]

It's not like HTML except for being XML which looks a lot like SGML.

XML does not only look a lot like SGML, it is a proper subset of SGML:

XML is an application profile or restricted form of SGML, the Standard Generalized Markup Language [ISO 8879]. By construction, XML documents are conforming SGML documents.

http://www.w3.org/TR/xml11/

[pluma]

Unlike HTML, btw, which started out as a loose subset of SGML but has abandoned the goal of SGML compatibility in favour of conceptual simplicity.

[dunham]

Interesting, I didn't realize they claimed XML was an SGML subset. I thought you couldn't express XML empty tags in an SGML DTD.