An application sends this message to IME window to specify style of the composition window. In contrast to Windows version 3.1, this message specifies the composition style of the current active input context. The IME user interface follows the style whenever it is given the input context.
lParam
Address of a COMPOSITIONFORM structure.
The IME user interface has a default style of composition window that is equal to the CFS_POINT style. If an application hasn't specified any composition style in its input context, IME User Interface retrieves the current caret position and window client area when it opens composition window. It is in client coordinates. The UI window does not receive this message.