Input processing can enter a "system modal" state. In this state, all pointing device and keyboard input is directed to a special window, known as the system-modal window, or to one of its child windows (or a window owned by one of them). An "owned" window is a window that refers to its owner window set by using either the hwndOwner parameter of the WinCreateWindow function or the hwndNewOwner parameter of the WinSetOwner function. All other main windows behave as though they are disabled and no interaction is possible with them.
Note: The disabled windows are not actually disabled, but made noninteractive. No messages are sent to these windows when the system-modal state is entered or left, and their WS_DISABLE style bits are not changed.
Where a system-modal window exists and another window is explicitly made the active window, the newly activated window becomes the system-modal window. This replaces the old one, which becomes a noninteractive window. When the system-modal window is destroyed, the system-modal state is ended, and input processing returns to its normal state.
This function should only be called while processing pointing device or keyboard input.
The new system-modal window is not locked during the processing of this function.