How does the browser know the set of pages to be cached for a particular offline app, though? Do you have to provide a static sitemap at a known URL? But to support multiple apps deliverable from a single subdomain, you would need to specify the sitemap's URL in some webpage, perhaps as an attribute to some HTML element. So each sitemap would be a sort of Manifest which controls the Cache for an app.
By the way, the app's cache obviously ought to be isolated from other apps' caches, right? Especially if you let the user grant an enlarged cache as a per-app permission. And the user might want to clear the miscellany browser cache without clearing the app cache, so we had better give this Application Cache a distinct name.
That's a decent point about clearing the cache - it should be distinct from flushing assets indicated for offline use. That distinction could be drawn by determining whether or not each asset was served with stale-if-error.
By the way, the app's cache obviously ought to be isolated from other apps' caches, right? Especially if you let the user grant an enlarged cache as a per-app permission. And the user might want to clear the miscellany browser cache without clearing the app cache, so we had better give this Application Cache a distinct name.