In practice, installation in web browser would use a service worker and some hand written caching logic. Neither is declarative. In fact, declarative (https://e

In practice, installation in web browser would use a service worker and some hand written caching logic. Neither is declarative. In fact, declarative (https://en.wikipedia.org/wiki/Cache_manifest_in_HTML5 https://en.wikipedia.org/wiki/Cache_manifest_in_HTML5) variant of this functionality was deprecated because devs wanted more programatic way to "install" offline web apps. It's still sandboxed, and limited, so what's cached this way is perhaps easy to totally remove by the browser. But that's not because of the declarativeness, but because of sandboxing.