class MIME::Type::Columnar
A version of MIME::Type that works hand-in-hand with a MIME::Types::Columnar container to load data by columns.
When a field is has not yet been loaded, that data will be loaded for all types in the container before forwarding the message to MIME::Type.
More information can be found in MIME::Types::Columnar.
MIME::Type::Columnar is not intended to be created except by MIME::Types::Columnar containers.