Although most applications use frame windows to create their main windows and dialog windows, they are not limited to frame windows. Applications can create nonstandard frame windows and still use the standard frame controls, such as the title bar and system menu, within the nonstandard windows.

An application can create a nonstandard frame window either by subclassing a frame window or by creating a private frame-window class. An application that subclasses a frame window can intercept the messages sent to the window and process them in new ways. An application that creates private frame-window classes essentially rewrites the frame-window procedure. In either case, by creating nonstandard frame windows, the application gains much more control over the arrangement of frame controls in the frame window.

The messages WM_FORMATFRAME, WM_UPDATEFRAME, and WM_CALCVALIDRECTS control the arrangement of frame controls for applications that subclass the frame-window procedure. By intercepting these messages, an application can rearrange the frame controls in a frame window.

To maintain the size and position of frame controls, an application that creates private frame-window classes can use WinCreateFrameControls and WinCalcFrameRect. These functions provide capabilities that are similar to those provided by frame windows.