{description: 'Manage a terminology client cache on the server. A client that repeatedly validates or expands against the same value sets and code systems can register those resources with the server once, under a server-issued cache-id, and then refer to them by url on subsequent calls instead of re-sending them each time.\n\nThe protocol is explicit: the client calls this operation with mode=start to create a cache; the server allocates the cache and returns its identifier in the `cache-id` output parameter. The client then sends that identifier as the `X-Cache-Id` HTTP header on subsequent $validate-code and $expand requests. Resources are populated into the cache by sending them (as `tx-resource`, or as the primary `valueSet`/`codeSystem`) on those requests, or by front-loading them in the mode=start call.\n\nBy default a cache is sealed: it holds only the resources front-loaded at mode=start and does not grow. A client that wants the cache to accumulate resources as they are seen (needed for incremental population and batch front-loading) requests an unsealed cache by sending sealed=false at mode=start. The mode=start response always reports, in the `sealed` output parameter, which kind of cache was created. When finished, the client calls mode=end to release the cache (the server will otherwise time it out).\n\nA server releases a cache that has not been used for some time. Because a client''s own local caching can absorb its terminology work for long stretches, a client may still depend on a server-side cache it has not touched for a while; mode=check exists for this case. It reports whether the cache is still there, and checking counts as use, so a client that expects to go quiet can keep its cache alive by checking periodically. The response reports the server''s idle timeout, so the client can size that interval to the server rather than guessing.\n\nBecause the server owns the cache-id, it can authoritatively report when a client refers to a cache it does not have (never created, expired, or released): such requests fail with an OperationOutcome whose issue carries the code `cache-id-unknown` from http://hl7.org/fhir/tools/CodeSystem/tx-issue-type. This is distinct from a value set or code system genuinely not being found, so a client can tell a stale cache from an authoring error.\n\nThis operation affects server state and SHOULD be invoked with POST; servers MAY also accept GET for convenience.', package_name: hl7.fhir.uv.tools.r4, name: CacheControl, type: 'false', package_version: 1.2.0, class: operation, kind: operation, url: 'http://hl7.org/fhir/tools/OperationDefinition/cache-control', version: 1.2.0}