Recommend that a browser "reload" contacts the logical origin

[ithinkihaveacat]

Recommend that if the user hits the "reload" button in their browser, the browser will contact the logical origin (i.e. the URL that is visible in the browser's URL bar) to determine freshness.

(Currently not specified, but seem to be the expected behaviour, see e.g. 1, 2, 3.)

[lidel]

I feel a better design would be an ability to opt out from a forced freshness check for specified time.
Think how it is possible to cache HSTS settings in the browser by including a max-age option:

• "pressing F5 in web browser does not contact the logical origin until snapshot from SXG is max-age old"
  • max-age=0 would mean that pressing "reload" button will always contact the logical origin
  • Shift+F5 would ignore SXG just like it ignores the cache

The max-age approach is more flexible and accounts for use cases where people want to avoid sending HTTP traffic to logical origin by any means necessary (cc ipfs/in-web-browsers#121 @jimpick )