I have been thinking for quite some time about using XML for this. It is pure AST you can relatively conveniently author as text. Having nice syntax is a good

I have been thinking for quite some time about using XML for this. It is pure AST you can relatively conveniently author as text. Having nice syntax is a good thing, yet no matter what the syntax is, it ends up as an AST. And the structure of AST records and the ways they can be combined matters quite a lot, I would say more than text syntax. XML makes it visible and easy to experiment with without getting distracted by text syntax niceties.