/**
 * Compares two strings based on a specified order.
 * @param s1 The first string to compare.
 * @param s2 The second string to compare.
 * @param order Optional. A Map object representing the order of strings.
 *              The key is the string value, and the value is the order index.
 *              Strings with lower order index come before strings with higher order index.
 *              If omitted, strings are compared based on their natural order (localeCompare).
 * @returns A negative number if s1 should come before s2,
 *          a positive number if s1 should come after s2,
 *          or zero if s1 and s2 are equal.
 */
export declare function compare(s1: string | undefined, s2: string | undefined, order?: Map<string, number>): number;