| In the beginning was the SGML. Then we said it's too verbose. We named some subsets XML, HTML, XLSX. Then we said it's still too long. So we named some subsets Markdown, and YML. Then we said it's still too long, and made JSON. What's wrong with subsets? Ambiguity in naming things. https://martinfowler.com/bliki/TwoHardThings.html Is JSON the same as YML? NO. Norwegian? https://news.ycombinator.com/item?id=26671136 |
If anything, XML as an SGML subset is more verbose than SGML proper; in fact, getting rid of markup declarations to yield canonical markup without omitted/inferred tags, shortforms, etc. was the entire point of XML. Of course, XML suffered as an authoring format due to verbosity, which led to the Cambrian explosion of Wiki languages (MediaWiki, Markdown, etc.).
Also, HTML was conceived as an SGML vocabulary/application [1], and for the most part still is [2] (save for mechanisms to smuggle CSS and JavaScript into HTML without the installed base of browsers displaying these as content at the time, plus HTML5's ad-hoc error recovery).
[1]: http://info.cern.ch/hypertext/WWW/MarkUp/MarkUp.html
[2]: http://sgmljs.net/docs/html5.html