Given the odd tech-and-stitching grooves I get into here, however did I miss this 1998 article??
XML is a simplified dialect of SGML (Standard Generalized Markup Language). For those of you unfamiliar with SGML, it is an international standard (ISO-8879) for defining descriptions of the structure and content of documents in an electronic form. XML simplifies SGML by capturing about 80 percent of SGML’s functionality with only 20 percent of the complexity.
HTML, which is a description of the structure and content of a single type of document called a “Web page,” is just one instance of what can be created with SGML. In other words, if HTML is a single knit sweater, SGML and XML are how-to books on knitting. By learning XML, you can create sweaters, socks, leg warmers, or any kind of knitted apparel you want!
Not bad, though it misses the opportunity to capture the generative power of a single XML vocabulary. If instance:web page:sweater and model:HTML:sweater knitting pattern, then metamodel:XML:this. (Ooh, and maybe model building tool:XML schema IDE:this.)