docs: public StringBuffer getMessageKey(StringBuffer sb)
      {
          if (sb == null)
              sb = new StringBuffer();
          if (m_messageDataDescChildren != null)
          {
              for (String strKey : m_messageDataDescChildren.keySet())
              {
                  MessageDataDesc messageDataDesc = m_messageDataDescChildren.get(strKey);
                  messageDataDesc.getMessageKey(sb);
              }
          }
          return sb;
      }