2.4.3 focus order - activedescendant

>
> *"An example of keyboard navigation that is not the sequential navigation
> addressed by this Success Criterion is using arrow key navigation to
> traverse a tree component. The user can use the up and down arrow keys to
> move from tree node to tree node. Pressing the right arrow key may expand
> a node, then using the down arrow key, will move into the newly expanded
> nodes. This navigation sequence follows the expected sequence for a tree
> control - as additional items get expanded or collapsed, they are added or
> removed from the navigation sequence."*
>

After reading that quote from Understanding 2.4.3, is there room for a Aria
technique for activedescendant? The primary use for this attribute is with
widgets like tree, combobox, and the like, where sequential navigation is
not relevant.

Can anyone think of an example where activedescendant would help to satisfy
2.4.3?