The Visibility Handler is responsible for listening out for document level visibility change events.
This includes visibilitychange if the browser supports it, and blur and focus events. It then uses
the provided Event Emitter and fires the related events.
The Visibility Handler is responsible for listening out for document level visibility change events. This includes
visibilitychangeif the browser supports it, and blur and focus events. It then uses the provided Event Emitter and fires the related events.