Describe spec features with more examples

[jkarlin]

The spec doesn't describe what the purpose of tags are (and its potential size limitations), how one might use getTags, and the proper way to "unregister" an event.

[jakearchibald]

I'm working on this

[jakearchibald]

Added more examples - https://github.com/WICG/BackgroundSync/compare/master...jakearchibald:adding-examples?expand=1

Will send a PR once bikeshed's web API is back up (I got a big bag of errors trying to install it on OSX).

As for the size limitations of tags, what are our limits? Should we add this to the formal part of the spec?

[jkarlin]

Chrome is 10240 characters at the moment. Not sure if that's something that should be defined in a spec or not.

[clelland]

We should consider specifying a minimum size, at least. Defining an exact size seems wrong, but maybe define what happens if you exceed whatever limit the UA sets.

[mkruisselbrink]

Getting more and more off topic for this issue, but in addition to specifying a minimum tag size browsers should support, do we also want to specify a minimum number of concurrent syncs/origin a browser should support (and what happens if a website tries to register too many syncs)? Similar to this section in the geofencing spec, but probably with higher numbers.