A WindowDisplayed message is added to the message queue when a window is displayed for the first time or after being hidden or minimized.

Windows are displayed when users click on their icons, and when programs call XgrDisplayWindow() . 

A WindowHidden message is added to the message queue when a window is hidden from view or minimized.

Windows are hidden when programs call XgrHideWindow() . 

A WindowKeyDown message is added to the message queue when the system detects a keyboard key down event.

window contains the window number of the currently selected window, which is the window with keyboard focus.

x,y contain the position of the mouse cursor in the local coordinates of focusGrid when the WindowKeyDown event was detected.

state identifies the depressed key and gives the state of the keyboard mode-keys (Alt-Control-Shift) when the WindowKeyDown event was detected.

time contains the value of the system millisecond time when the WindowKeyDown event was detected.

In some programs, individual grids need to receive key down messages. Furthermore, windows can contain several grids capable of accepting keyboard focus. In these cases, window functions keep track of the grid that most recently had keyboard focus in each window and send it a KeyDown message when it receives WindowKeyDown . The WindowKeyDown message must not be passed to the grid function, because WindowKeyDown is a window message and window messages must not be sent to grid functions.