SHOULD in a note and enabled by default

[annevk]

https://wicg.github.io/BackgroundSync/spec/#permission has a requirement in a note. That doesn't work.

As per #107 and #37 it's also not clear to me what "enabled by default" means, as our (Mozilla's) best plan to date to avoid surprises is to prompt in certain cases.

[jakearchibald]

The model here is supposed to be similar to similar to sendBeacon(), in that it's used whether the user is offline or not, but it will handle the offline case. Although I recognise that it can do more than sendBeacon().

The assumption was, if the user visited the site as a top-level origin, they'd be happy with a one-off sync unless they'd expressed otherwise.

I agree this is not well presented in the spec, and of course browser should be free to behave differently.

[annevk]

Yeah, we want to prompt when offline, as the user might not want to reveal their destination (if any). And as per #37 we might want to prompt or auto-deny under certain network/battery conditions.

[martinthomson]

I might have a different view on that. I might want to just have it not work in that case, because annoying people about things that shouldn't bother them is inconsiderate.

[annevk]

Well, having to remember to navigate to the site once online to get your offline work in the cloud is also not ideal. "Would you like X to know when you're next online so they can save your work?" does not seem overly obtrusive to me.