I have a file of great quotes from wise people. A minority of those are about technology, and a minority of the technology ones are about XML or SGML. Here is one from an ACM piece that Michael did at https://queue.acm.org/detail.cfm?id=1103834:

In XML, data can have an elaborate and intricate structure that is significantly richer and more complex than a table of rows and columns. Calling this semi-structured is misleading, just as it would be to describe DNA molecules as semi-structured because they are less simply regular than those of table salt. XML seeks to make possible capturing and expressing the structure of the data as we understand it, without forcing it into a too-simple structure.

The perfect levels of abstraction and the references to table salt and DNA were just so Michael. I will not forget him.