title: Questions about QuickFIX message cracking
body: <p>VERY basic questions from a FIX newbie</p>
  
  <p>Looking at the documentation at <a href="http://www.quickfixengine.org" rel="noreferrer">http://www.quickfixengine.org</a> and reading posts here on stackoverflow I see lots of talk about message 'cracking'. I think I sort of get the idea, but  feel like I'm still not totally clear.</p>
  
  <p>Can some explain in general what exactly this is (why is it necessary? it sounds like a hack), why it only seems relates to received FIX messages, and is not used at all when using Python? </p>
  
  <p>Thank you!</p>