code: def distinguished_folder_id!(dfid, change_key = nil, act_as = nil)
        attribs = {'Id' => dfid.to_s}
        attribs['ChangeKey'] = change_key if change_key
        @nbuild[NS_EWS_TYPES].DistinguishedFolderId(attribs) {
          if ! act_as.nil?
            mailbox!({:email_address => act_as})
          end
        }
      end
docs: Build the DistinguishedFolderId element
   @see http://msdn.microsoft.com/en-us/library/aa580808.aspx
   @todo add support for the Mailbox child object