It seems like there are some restrictions on them, but they are kind of vague about exactly how restrictive they are. > Sync events will often complete while t

It seems like there are some restrictions on them, but they are kind of vague about exactly how restrictive they are. > Sync events will often complete while the user has a page open to the site, so requiring user permission would be a poor experience. Instead, we’re limiting when syncs can be registered and triggered to prevent abuse. E.g.: > You can only register for a sync event when the user has a window open to the site. > The event execution time is capped, so you can’t use them to ping a server every x seconds, mine bitcoins or whatever.