import type { DateTimeDurationUnit, Overflow } from "../../types/index.js";
/**
 * Add a temporal amount to a UTC datetime string and return a new UTC Instant string.
 *
 * - Uses Temporal.Instant.from to parse, adds duration, returns new Instant.
 * - Validates duration units and values.
 * - Returns "" for invalid input.
 *
 * `overflow` ("constrain" (default) | "reject") controls out-of-range results, e.g. adding 1 month
 * to Jan 31: "constrain" clamps to Feb 29/28, "reject" throws (resulting in "").
 *
 * @param value ISO UTC datetime string (e.g. "2024-03-10T12:00:00Z")
 * @param units Partial<Record<DateTimeDurationUnit, number>> object specifying units to add
 * @param options optional: overflow ("constrain" | "reject")
 * @returns UTC Instant string after addition, or "" on invalid input
 *
 * @example addUtc("2024-03-10T12:00:00Z", { days: 5 }) // "2024-03-15T12:00:00Z"
 * @example addUtc("2024-03-10T12:00:00Z", { months: 1, years: 1 }) // "2025-04-10T12:00:00Z"
 * @example addUtc("invalid", { days: 5 }) // ""
 */
export declare function addUtc(value: string, units: Partial<Record<DateTimeDurationUnit, number>>, options?: {
    overflow?: Overflow;
}): string;