What is Notification.Type.ASSISTIVE_NOTIFICATION?

The first four `Notification.Type` types work for me.

Notification.Type.HUMANIZED_MESSAGE
Notification.Type.TRAY_NOTIFICATION
Notification.Type.WARNING_MESSAGE
Notification.Type.ERROR_MESSAGE
Notification.Type.ASSISTIVE_NOTIFICATION

But the `Notification.Type.ASSISTIVE_NOTIFICATION` does nothing for me when running in Safari browser in Mac OS X Mountain Lion.

I cannot find any description of behavior for this particular type in either the class doc or in the Book Of Vaadin. 

Hi, Position.ASSISTIVE javadoc specifies that it is a notification that is only rendered for users of assistive technologies (eg. screen readers.) One use case is changes to application state that are visually obvious but not so much if you cannot see.

Type.ASSISTIVE_NOTIFICATION should certainly be documented as well.