class Net::IMAP::AppendUIDData

or IMAP4rev2 capability.
Requires either UIDPLUS [RFC4315]
== Required capability
reports UIDNOTSTICKY.<br>append command—unless the target mailbox
AppendUIDData inside every TaggedResponse returned by the
A server that supports UIDPLUS (or IMAP4rev2) should send
APPENDUID response code.
AppendUIDData represents the ResponseCode#data that accompanies the
Config#parser_use_deprecated_uidplus_data to false.
0.6.0 release.</em> To use AppendUIDData before 0.6.0, set
NOTE: <em>AppendUIDData will replace UIDPlusData for APPENDUID in the
>>>

def initialize(uidvalidity:, assigned_uids:) 

def initialize(uidvalidity:, assigned_uids:)
  uidvalidity   = Integer(uidvalidity)
  assigned_uids = SequenceSet[assigned_uids]
  NumValidator.ensure_nz_number(uidvalidity)
  if assigned_uids.include_star?
    raise DataFormatError, "uid-set cannot contain '*'"
  end
  super
end

def size

Returns the number of messages that have been appended. 
def size
  assigned_uids.count_with_duplicates
end