See also: Data Tables
...
Generally the focus will behave as in other Forms.
...
There is one variation on this behavior: When the focus is on the Chosen items list, and the user moves one or more selected items to the bottom of the list, the focus will move to the Up arrow (9) (instead of to the next focusable element).
If the user moves all the items from the chosen items list back to the available items list, the focus will automatically move from the left move button (5) to the the right move button (4).
...