title: What are "bodyLength" and "checkSum" in QuickFix?
body: <p>Anyone here can tell me what are "bodyLength" and "checkSum" in QuickFix? </p>
  
  <p>I have searched on <a href="http://www.quickfixengine.org/quickfix/doc/html/namespace_f_i_x_1_1_f_i_e_l_d.html#aac36b44ae2683cdf53dd263b82e735d1" rel="nofollow">this</a> and there is no definition. </p>
  
  <p>What is the purpose of those in Message (tag = 9 and 10)?</p>