There is no concept of a "focus controller" currently available. The existing FocusModel class is only available for table/list/tree components. There should be a means for better control over keyboard focus, particularly for customising keyboard focus traversal.
For example - the Ensemble demo app has a network proxy dialog. While the dialog is visible, it is still possible to focus on nodes in the main app by tabbing. Ideally it should be possible to restrict focus traversal to just the proxy node.