property nextSelectedData

This property returns a reference to the next selected data row in the case of multi-selection. Returns null object if no additional selected items are present. Please note that you should always call firstSelectedData prior to using this property.

var list = scene.getBoxById("myList");
if (list)
{
    var sel = list.selection;
    if (sel)
    {
        var selData = sel.firstSelectedData;
        while (selData)
        {
            Foo(selData); // process data row
            selData = sel.nextSelectedData;
        }
    }
}