Makes the succeeding item current. If the current item before this function call was the last item, the current item will be set to null. If the current item was null, this function does nothing. Assigns list to this list and returns a reference to this list. This list is first cleared, then each item in list is appended to this list.
Returns null if the current item is null or equal to the first item.
Makes the preceding item current. If the current item before this function call was the first item, the current item will be set to null. If the current item was null, this function does nothing. The removed item is deleted if auto-deletion is enabled. The item after the removed item becomes the new current list item if the removed item is not the last item in the list.