/**
 * A function that returns a `Date` object of the first year in a decade.
 *
 * @param date - The start date value.
 * @returns - The first year in a decade.
 *
 * @example
 * ```ts-no-run
 * firstYearOfDecade(new Date(2017, 0, 1)); // 2010-1-1
 * firstYearOfDecade(new Date(2007, 10, 22)); // 2000-11-22
 * firstYearOfDecade(new Date(2026, 0, 1)); // 2020-1-1
 * ```
 */
export declare const firstYearOfDecade: (value: Date) => Date;