its quite a lot older than that! http://xml.coverpages.org/linuxml-19990226.html http://xml.coverpages.org/linuxml-19990226.html is the first one I've heard of,

its quite a lot older than that! http://xml.coverpages.org/linuxml-19990226.html http://xml.coverpages.org/linuxml-19990226.html is the first one I've heard of, but I wouldn't be surprised if there are predecessors decades older still. The problem largely still is the effort of rewriting all/enough userspace tools to actually use the type system to make it worthwhile, or the even less appealing approach of maintaining parsers/shims/wrappers for things that allow it to work.