The system maintains a minimum and maximum tracking size for a window of the WS_THICKFRAME style; a window with this style has a sizing border. The minimum tracking size is the smallest window size you can produce by dragging the window's sizing border. Similarly, the maximum tracking size is the largest window size you can produce by dragging the sizing border.
A window's minimum and maximum tracking sizes are set to system-defined default values when the system creates the window. An application can discover the defaults and override them by processing the WM_GETMINMAXINFO message. For more information, see Size and Position Messages.