https://github.com/slightlyoff/BackgroundSync/blob/master/explainer.md has a design document for enabling web pages to perform synchronization in the background. This bug pertains to periodic synchronization. When granted (perhaps persistently) the web page can synchronize some data in the background through a service worker when the user is not visiting the web page. This allows the site to update itself and remain fresh so that when the user next visits less network activity is required. This has implications for battery life, privacy (e.g. geolocation through IP addresses), and perhaps exceeds what users think a page is capable of.
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