There’s another repo, the Pkl Pantry, that provides a couple of ready made templates (Schemas) that you can try out: https://github.com/apple/pkl-pantry
I was looking for a translation from a pkl template into an xml schema. It would probably be lossy - I think pkl can express more invariants than xml or json schema can - but still gives some invariants on the data for use downstream of the pkl tooling.
There’s another repo, the Pkl Pantry, that provides a couple of ready made templates (Schemas) that you can try out: https://github.com/apple/pkl-pantry