The classes in this package are used for development of accessibility service that provide alternative or augmented feedback to the user.
AccessibilityService runs in the background and receives callbacks by the system when
AccessibilityEvents are fired. Such events denote some state transition in the user interface, for example, the focus has changed, a button has been clicked, etc. Such a service can optionally request the capability for querying the content of the active window. Development of an accessibility service requires extends this class and implements its abstract methods.