code: public void addMessageDataDesc(MessageDataParent messageDataDesc)
      {
          if (messageDataDesc instanceof MessageFieldDesc)
          {
              if (m_messageDataDesc == null)
                  m_messageDataDesc = new MessageRecordDesc(this, Constant.BLANK);
              m_messageDataDesc.addMessageDataDesc(messageDataDesc);
          }
          else
          {
              m_messageDataDesc = (MessageDataDesc)messageDataDesc;
              if (m_messageDataDesc != null)
                  m_messageDataDesc.setMessageDataParent(this);
          }
      }
docs: Add a child message data desc.