/**
 * Verify an ID is a valid ID.
 */
export declare function verifyId(id: string): string;
/**
 * an accessor for getting ids from node data
 *
 * The accessor must return an appropriate unique string id for given datum.
 * This operator will only be called once for each input.
 *
 * `index` will increment in the order data are processed.
 *
 * This is used in {@link Stratify#id}, {@link Connect#sourceId}, and
 * {@link Connect#targetId}.
 */
export interface Id<in Datum = never> {
    /**
     * get node id from a datum
     *
     * @param datum - the datum to get the id from
     * @param index - the index that the data was encountered in
     * @returns id - the id corresponding to the node datum
     */
    (datum: Datum, index: number): string;
}