(0) Always load from network and do not check if the cache has a valid entry (similar to the "Reload" feature in browsers). In addition, force intermediate caches to re-validate.
(1) Load from the network if the cached entry is older than the network entry. This will never return stale data from the cache, but revalidate resources that have become stale.
(2) Load from cache if available, otherwise load from network. Note that this can return possibly stale (but not expired) items from cache.
(3) Only load from cache, indicating error if the item was not cached (i.e., off-line mode).