Perhaps we should add an appendix to help people do this?
FYI/FWIW I've just implemented this spec via a service worker.
It would be nice if the spec clarified and defined the following. (I deduced it from @kazuho 's server and serviceworker implementations.)
... base64 ...; complete
Additionally more examples would be welcome, to aid implementors in validating their support. In particular the etags concatenation is unclear to me from the referenced spec.