XML is a simplified version of SGML (ISO 8879). XML inherited some of the power of SGML as well as some of its weaknesses.

XML also lost some of SGMLs power (if you known SGML I am thinking of features like CONCUR, CONREF, Link Process Definitions and RANK.)

This list is a discussion area aimed at pursuing the idea that SGML is too simple. What is needed is a level above SGML that makes SGML and XML simply special cases of a "de-quantized architecture".

The core idea is that everything about a physical markup language can be expressed in purely quantum terms - Quantum Markup Language - or QML for short.

An instantiation of QML happens at the point where someone looks at it and the quantum states degenerate to yield a Newtonian Concrete Syntax. Effectively all current markup langauges are instances of NML derived from QML by means of observation.