An application sends an LB_SETCARETINDEX message to set the focus rectangle to the list box item at the specified index in a multiple-selection list box. If the item is not visible, it is scrolled into view.
wParam
Specifies the zero-based index of the list-box item to receive the focus rectangle.
lParam
This parameter is not used.
The return value is LB_ERR if an error occurs.
LB_GETCARETINDEX