 * MimeTreeParser::MessagePartList
  * MimeTreeParser::MimeMessagePart
   * MimeTreeParser::TextMessagePart
    * MimeTreeParser::MessagePart
   * MimeTreeParser::EncapsulatedRfc822MessagePart
    * MimeTreeParser::MimeMessagePart
     * MimeTreeParser::AttachmentMessagePart
      * MimeTreeParser::MessagePart
     * MimeTreeParser::AttachmentMessagePart
      * MimeTreeParser::MessagePart
