By DSL I mean something like how HTML is used to make websites. HTML was derived from SGML, and is related loosely to XML, but does not contain a lot of the complexities of XML.

I do not mean JSON, as JSON is not a good generalized meta-programming notation. People use it that way but it ends up ugly and hard to read.

JSON can be used alright as a configuration notation, but does not represent itself well as a metaprogramming language, since it does not preserve order or allow mixed content. You can get order by using an array of course, but it is much more verbose than the equivalent content in XML or HTML.

You might say, by DSL, I mean "custom markup languages".