Chapter 5: The Document/View Architecture Visual C++ and MFC Fundamentals
When using an MDI application, a user can create a document, open another while the
first is still displaying, and even create new documents or open additional ones. The
documents are stacked in a Z-order axis of a 3-D coordinate system. There are two ways
to display the documents of an MDI. If one document is maximized, all documents are
maximized. In this case, the main menu of the application would display the system
buttons on its right, which creates two ranges of system buttons:If no document is maximized, each document can assume one of two states: minimized or
restored. While the child documents are confined to the borders of the main frame, if a
document is or gets minimized, it would display its button inside the main frame. If a
document is not minimized, it would display inside the main frame either with its original
size or the size the user had given it: