Determines the list-box item nearest the point specified in pt.
Point for which to find the nearest item, specified relative to the upper-left corner of the client area of the list box.
Reference to a BOOL variable which will be set to TRUE if pt is outside the client area of the nearest list box item, FALSE if pt is inside the client area of the nearest list box item.
The index of the nearest item to the point specified in pt.
You could use this function to determine which list-box item the mouse cursor moves over.