The classes in this package are used for development of accessibility service that provide alternative or augmented feedback to the user.
  An 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.
  An AccessibilityServiceInfo describes an
  AccessibilityService. The system notifies an
  AccessibilityService for AccessibilityEvents
  according to the information encapsulated in this class.
| AccessibilityService | An accessibility service runs in the background and receives callbacks by the system
 when AccessibilityEvents are fired. | 
| AccessibilityServiceInfo | This class describes an AccessibilityService. |