See etirelli comment here.

We need to add support for Boxed Lists.

See "10.2.1.5 Boxed List" in the DMN1.2 Specification.

etirelli Please confirm it's sufficient to support vertical boxed lists?

Furthermore can you please confirm a "Boxed List" can be used everywhere an Expression can be used. I see List extends Expression however want to be sure there's not an edge case etc tucked away that you know of