title: Why isn't ETag alone enough to invalidate the browser cache?
body: <p>I've read a lot of related articles on the matter and also the very good article about HTTP caching here:
  <a href="https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/http-caching?hl=en#invalidating-and-updating-cached-responses" rel="noreferrer">https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/http-caching?hl=en#invalidating-and-updating-cached-responses</a>
  but it is still not clear to me:</p>
  
  <p>Why isn't sending an ETag header enough to invalidate the browser cache for a particular resource? Why does everyone recommend actually changing the URL/filename of the resource to force the browser to re-download the file? If the browser has already cached the file with a particular ETag and the ETag is modified on the server, wouldn't that suffice?</p>