Base class for defining in which direction the focus moves in a focus ring.
Focus ring implementations can move the focus in various direction; they can derive from this class to formalize the various ways the focus can change from one element to the other.
| lastValue | Last value for the direction defined by this class. |
| none | The null direction. This is usually used when the focus stays on the same element. |
| unspecified | Focus came from an unspecified direction, for example after a mouse down. |