An IME sends this message to a soft keyboard window to specify the subtype to use for displaying the reading characters of a key in the soft keyboard window. It also can be used for an IME-specific purpose.
lParam
Soft keyboard subtype.
The UI window does not receive this message. The SOFTKEYBOARD_TYPE_T1 does not use this information. The IME sends the message to the soft keyboard. It not change the displaying of the reading characters. An IME that uses the SOFTKEYBOARD_TYPE_T1 soft keyboard can freely define the meaning of this message. The IME can get this data by using IMC_GETSOFTKBDSUBTYPE.