WM_DESTROY

This message informs the window that it is being destroyed. The DestroyWindow function sends the WM_DESTROY message to the window after removing the window from the screen. The WM_DESTROY message is sent to a parent window before any of its child windows are destroyed.

Comments

If the window being destroyed is part of the clipboard-viewer chain (set by using the
SetClipboardViewer function), the window must remove itself from the clipboard
viewer chain by processing the ChangeClipboardChain function before returning from the WM_DESTROY message.