Haha, that certainly works. It brings up the question of "what Arc internals should people need to know about?". I've never looked into Arc's tagged types until this issue.
My answer to that question has always been, "it depends." The anti-encapsulation ethos (homoiconicity, using lists where other languages may use objects, the entire compiler fitting in one file and being accessible front-and-center, etc.) means that there's always the ability to peel back another layer of the onion when it becomes relevant.
I think it's a documentation issue. I think I had to search the forums to find out about it when I was playing with JSON interop. Nowhere on the actual template page in the Arc documentation does it tell you this is a thing.
Some things I've only been able to figure out by studying the compiler or arc source code itself. Granted, that's illuminating, but it's also sometimes really annoying.
Indeed. It never occurred to me to write about this. Would you be interested in writing something up? I can help you wrestle with the documentation system if you like.