sItemStart (SHORT)
If the list box allows multiple selected items, that is, if it has a style of LS_MULTIPLESEL, then this parameter indicates the index of the item from which the search for the next selected item is to begin. Therefore, to get all the selected items of the list, this message is sent repeatedly, each time setting this parameter to the index of the item returned by the previous usage of this message.
If this parameter is set to LIT_CURSOR the index of the item in the list box which currently has the cursor is returned.
If the list box only allows a single selection, this parameter is ignored.
LIT_CURSOR