Overlap with Web Manifests

[quasicomputational]

What's the relation between this spec and Web Manifests?

There seems to be an awful lot of overlap, with the major differences being:

1. Web Manifests collect many resources together (e.g., an entire newspaper website), while Content Index applies to individual resources (e.g., single newspaper articles).

2. Web Manifests are discovered declaratively, while Content Index is used via scripting. However, both still need scripting to actually install the service worker for offline use. This allows Content Index to be kept in sync with the state of the offline cache, so that only items that are actually available (and useful) offline are shown to the user.

3. Web Manifests don't have a way to explicitly indicate that they're useful offline; while many will be, there will inevitably be some that strictly need the network (e.g., real-time multiplayer games).

Some sort of compare-and-contrast probably belongs in the spec, as well as notes on why extending Web Manifests (e.g., with an offline boolean field) wouldn't be as good.

I also think that it could lift some design directly from the Web Manifest spec, which has basically the right approach to responsive icons (#2) and, less perfectly but still better, to categories (#7) and i18n (#6).