They describe three types of markup. Seems kinda arbitrary, but a curious line of thought - I enjoyed the article. It made me imagine a new kind of hypertext,

They describe three types of markup. Seems kinda arbitrary, but a curious line of thought - I enjoyed the article. It made me imagine a new kind of hypertext, an evolution of HTML that unifies all these realms and more as a universal templating language. One can dream! > Red markup describes how to present something. One way to spot presentational markup is that it usually doesn't make sense if you imagine changing from one media to another (if it's a print/web document, imagine translating it into an audio recording). > Yellow markup describes the structure of the document itself. To spot structural markup, replace the content (or compare multiple documents in the same format) and see what labels are stable. You can also imagine porting the content to another format (article, book, slide show, and so on) and consider what would break. > Blue markup describes the ontology of things that appear in the content--it names and categorizes them.