import type { CmcdKey } from './CmcdKey.js';
/**
 * Check if a key is a custom key.
 *
 * @param key - The key to check.
 *
 * @returns `true` if the key is a custom key, `false` otherwise.
 *
 * @group CMCD
 *
 * @beta
 */
export declare function isCmcdCustomKey(key: CmcdKey): boolean;
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