/**
 * Thrown when a lookup names a rule or group that does not exist.
 *
 * ```ts
 * try {
 *   await engine.runGroup("cor", ctx);
 * } catch (err) {
 *   if (err instanceof UnknownLookupError && err.kind === "group") {
 *     // a typo, not a failed evaluation
 *   }
 * }
 * ```
 */
export declare class UnknownLookupError extends Error {
    /** Whether the missing thing was a rule name or a group label. */
    readonly kind: "rule" | "group";
    /** The name or label that matched nothing. */
    readonly key: string;
    constructor(kind: "rule" | "group", key: string);
}