Allow type checking for sub-objects of multipart/form-data objects

[RealmyTheMan]

What is the problem this feature would solve?

One might accept file uploads in a route like so:

({ body: t.Object({ files: t.Files() }) })

This will (naturally) only work with the "multipart/form-data" format. But this also makes it lose JSON-specific features, such as this, which might be necessary in some scenarios:

({
  body: t.Object({
    files: t.Files(),
    subObject: t.Object({ example: t.String() }) // you can never set the value of "example", i tried
  })
})

What is the feature you are proposing to solve the problem?

What if "sub-objects" (or arrays) under the body object were parsed as a JSON string (and checked against the type) when the request uses multipart/form-data?

What alternatives have you considered?

I can run JSON.parse() myself of course, but it wouldn't automatically work with the type checking system, and I'd have to do it manually.