About ImeSetCompositionString

If the IME does not have the capability of ImeSetCompositionString, it does not specify any SCS capability in the IMEINFO structure. If the IME can handle ImeSetCompositionString, it sets the SCS_COMPSTR bit. If the IME can generate the reading string from the composition string, it may set the SCS_CAP_MAKEREAD bit.

If the IME has the SCS_CAP_COMPSTR capability, ImeSetCompositionString will be called. The IME takes the new composition string from the application and generates the WM_IME_COMPOSITION message.

If the IME has SCS_CAP_MAKEREAD capability, it can make the reading string from the composition string.