import type { DateTimeDurationUnit, Overflow } from "../../types/index.js";
/**
 * Return a PlainDateTime ISO string with `units` added to `value`.
 *
 * - Validates `value`, `units`, and `amount` before performing the add.
 * - Returns "" for invalid inputs.
 *
 * `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 PlainDateTime string
 * @param units Partial<Record<DateTimeDurationUnit, number>> object specifying units to add
 * @param options optional: overflow ("constrain" | "reject")
 * @returns ISO PlainDateTime string after addition, or "" on invalid input
 *
 * @example addDateTime("2024-03-10T12:00:00", { days: 5 }) // "2024-03-15T12:00:00"
 * @example addDateTime("invalid", { days: 5 }) // ""
 * @example addDateTime("2024-01-31T12:00:00", { months: 1 }, { overflow: "reject" }) // ""
 */
export declare function addDateTime(value: string, units: Partial<Record<DateTimeDurationUnit, number>>, options?: {
    overflow?: Overflow;
}): string;