Note: This feature is available in Web Workers
Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.
The tag read-only property of the Notification interface signifies an identifying tag for the notification, as specified in the tag option of the Notification() constructor.
The idea of notification tags is that more than one notification can share the same tag, linking them together. One notification can then be programmatically replaced with another to avoid the users' screen being filled up with a huge number of similar notifications.