Singleton as a List of NestedTypes? #446

Is there a way to define a singleton as a list of nested types?

For example, say you have a YML which only has a list of objects at the root level (no keys, just items):

# categories.yml

- id: categoryA
  name: Category A

- id: categoryB
  name: CategoryB

- id: categoryC
  name: Category C

Doesn't look like there's a way to define that document as-is.

It's not really a big deal though, as the YML could be modified to put the list inside a named key as a workaround.

# categories.yml

categories:
  - id: categoryA
    name: Category A
  
  - id: categoryB
    name: CategoryB
  
  - id: categoryC
    name: Category C

It's possibly not be a very common use-case though.