Ask HN: Example of your favorite CSV Schema Documentation?

I've been working on an interface that accepts csv, and have been struggling to find good examples of services that have solid definitions of acceptable schema (column names, types, Required/Optional/Constriants).

I'd also be interested in examples that have documented nested arrays, nested objects, or nested object arrays in csv.

I've been thinking about it alot since openAPI/GQL really do solve documentation, and can even autogen from views, but i haven't found something similar for CSV.