Every vocabulary the API validates against, with the value-space of each — closed (the complete authoritative set, safe to switch on), observed (a dated measurement of what the corpus currently holds, never an allowlist) and identifier (a key with a format and a resolver, never enumerated). Carries a sha256 you can pin and diff in CI to detect a vocabulary change before it reaches your code. Requires a key so use stays attributable, and is NOT metered — checking a value before spending a query unit should not cost a query unit.