The WM_IME_STARTCOMPOSITION message is sent immediately before the IME generates composition string as a result of a key stroke. The message is a notification to an IME window to open its composition window. An application should process this message if it displays composition characters itself.
No return value.
The wParam and lParam parameters are not used.
If an application has created an IME window, it should pass the WM_IME_STARTCOMPOSITION message to that window. The DefWindowProc function processes this message by passing it to the default IME window.