cacheDuration property

The client-side cache duration.

The client MUST add this duration to the current time to determine the expiration time. The expiration time then applies to every hash prefix queried by the client in the request, regardless of how many full hashes are returned in the response. Even if the server returns no full hashes for a particular hash prefix, this fact MUST also be cached by the client. Important: the client MUST NOT assume that the server will return the same cache duration for all responses. The server MAY choose different cache durations for different responses depending on the situation.