Windows multiple document interface (MDI) provides applications with a standard interface for displaying multiple documents within the same instance of an application. An MDI application creates a frame window which contains a client window in place of its client area. An application creates an MDI client window by calling CreateWindow with the class MDICLIENT and passing a CLIENTCREATESTRUCT data structure as the function's lpParam parameter. This client window in turn can own multiple child windows, each of which displays a separate document. An MDI application controls these child windows by sending messages to its client window.
The MDI functions include:
| Function | Description |
| ArrangeIconicWindows | Arranges minimized (iconic) child windows |
| DefMDIChildProc | Provides default processing those for MDI child window messages an that application does not process |
| TranslateMDISysAccel | Processes multiple document interface (MDI) child window command accelerators |