The dispatch ID of the event fired by the control.
Pointer to a member function that handles the event. This function should have a BOOL return type, and parameter types that match the event's parameters (see vtsParams). The function should return TRUE to indicate the event was handled; otherwise FALSE.
A sequence of VTS_ constants that specifies the types of the parameters for the event. These are the same constants that are used in dispatch map entries such as DISP_FUNCTION.