title: Splitting the main message map (BEGIN_MSG_MAP_EX) into two files
body: <p>I'm experimenting with WTL, and I'd like to separate a large message map to two or more files. For example, I'd like to move the tray icon logic into a separate file. I'm aware of <code>CHAIN_MSG_MAP</code> and <code>CHAIN_MSG_MAP_MEMBER</code>, but what should I use in this case?</p>
  
  <p>Also, how will I be able to access the window handle from the second class?</p>