This was intentionally not added — but we should probably call out in the documentation why:

RFC822 is functionally equivalent to BODY[], and I’d argue that we should just return it as such, e.g. treat a RFC822 in the response as a BODY[] response.

Similarly RFC822.HEADERmaps to BODY.PEEK[HEADER] and RFC822.TEXT maps to BODY[TEXT].

These exist in the IMAP specs for historical reasons — old IMAP standards (pre version 4) had these, and that historical luggage was kept, while adding the more flexible BODY… attributes. For NIOIMAP, we should just always use BODY….