[Many new and intermediate users find it difficult to learn to use MDI applications. Therefore, you should consider other models for your user interface. However, you can use MDI for applications which do not easily fit into an existing model.]
The multiple-document interface (MDI) is a specification that defines a user interface for applications that enable the user to work with more than one document at the same time.
Provides default processing for any window messages that the window procedure of a MDI frame window does not process. All window messages that are not explicitly processed by the window procedure must be passed to the DefFrameProc function, not the DefWindowProc function.
Provides default processing for any window message that the window procedure of a MDI child window does not process. A window message not processed by the window procedure must be passed to the DefMDIChildProc function, not to the DefWindowProc function.
Processes accelerator keystrokes for window menu commands of the MDI child windows associated with the specified MDI client window. The function translates WM_KEYUP and WM_KEYDOWN messages to WM_SYSCOMMAND messages and sends them to the appropriate MDI child windows.
Sent to a MDI client window to maximize an MDI child window. The system resizes the child window to make its client area fill the client window. The system places the child window's window menu icon in the rightmost position of the frame window's menu bar, and places the child window's restore icon in the leftmost position. The system also appends the title bar text of the child window to that of the frame window.