1) Uncached range requests starting from 0 are filled from origin starting from 0. The response is cached.
2) Uncached range requests starting from > 0 are proxied to the origin with the requested range. This means that uncached range requests can always be served immediately without waiting for the file to fill from the beginning. However, this partial response from the origin, is NOT cached.
3) Cached range requests are served from cache, returning the requested ranges.
In all scenarios, you will get a 206 Partial Content response.