import type { TimeUnit } from '../unit';
/**
 * Type guard: returns `true` only when `unit` is a canonical `TimeUnit`.
 * Aliases (e.g. `'day'`, `'sec'`) are rejected — use `timeUnitFromAlias`
 * to resolve aliases to canonical values first.
 *
 * @param unit		Value to validate as a canonical time unit.
 * @returns			true 	-	`unit` is a canonical `TimeUnit`.
 *					false	-	`unit` is not a canonical `TimeUnit`.
 *
 * @category Time Units
 */
export declare function timeUnitSupported(unit?: unknown): unit is TimeUnit;