== Advantages ??? == 
 "Possibly faster and more memory efficient, since the application is shared, and only the document changes. the speed of switching between the internal windows is usually faster than having the OS switch between external windows." 

 I don't understand this, particularly "the application is shared." Sure the parent window is shared but multiple parent windows can be run by the same process. Also, on typical Windows applications, all windows are run by the OS (user32.dll). What make "internal windows" "usually faster?"