The IMN_OPENCANDIDATE message is sent to the application when an IME is about to open the candidate window. An application should process this message if it displays candidates itself. The application can retrieve a list of candidates to display by using the ImmGetCandidateList function. The application receives this notification message through the WM_IME_NOTIFY message.
fCandidate = (DWORD) lParam;
No return value.
By default, the IME window creates a candidate window when it processes this message.