There are the markdown and wiki formats. XML is a mark-up language. Most structured data just doesn't need to be marked up, so XML doesn't always make sense a

There are the markdown and wiki formats. XML is a mark-up language. Most structured data just doesn't need to be marked up, so XML doesn't always make sense and something like JSON does. Web content is often continuous text that does, indeed, need to be marked up. Occasionally, HTML is used to define a form or something that isn't continuous text. In those cases, the form html can be generated from the underlying data types in whatever language the application is written in or using a domain specific language that resembles JSON but represents HTML.