I remember in the hay days of XML, someone made an article that discussed why XML is really just a language of S-expressions. This article seems argue something similar.

P.S., S-expression or not, XML-based DSLs are horrible. I don't know how many people have PTSDs using ANT or a slew of commercial "user-friendly" DSLs for test automation, process automation, and etc. It turns out the companies just didn't know how to design small programming languages and certainly lacked of compiler-writing skills.