moveByOffset( offset , isSelecting, isSelectingRange)
Return type: no return value
If offset is positive, adjusts the focused item forward by that many items. If offset is negative, adjusts the focused item backward by that many items. If isSelecting is true, then the selection is also adjusted. If isSelectingRange is also true, then the new item is selected in addition to any currently selected items. If isSelectingRange is false, any existing selection is cleared. Items that are hidden are skipped.