The website’s comparisons to YAML and JSON confused me, because neither of those are a markup language, meaning a language for annotating a document.
I am not sure whether ArchieML is a markup language, like HTML and Markdown, or a data serialization language, like YAML and JSON. The example document looks mostly like a marked-up document, but all the syntax examples look like serialized data.
It wouldn’t be the first time a language ending with “ML” found out its name was wrong. Both YAML and TOML started out calling themselves a markup language, and then changed their acronym later, when they realized their mistake. “YAML Ain’t Markup Language”.
There is some discussion on markup languages vs. data serialization languages on the Stack Overflow question If YAML ain’t markup language, what is it?.