export interface FormatDurationOptions {
    style?: "long" | "short" | "narrow";
    zero?: boolean;
}
/**
 * Render an ISO 8601 duration string as a locale-aware, human-readable string.
 *
 * - Uses Temporal.Duration.from to parse, then Intl.NumberFormat({ style: "unit" })
 *   to render each nonzero year/month/week/day/hour/minute/second component with
 *   correct per-locale unit labels and pluralization, joined via Intl.ListFormat.
 * - Sub-second components (milliseconds/microseconds/nanoseconds) are folded into
 *   the seconds component as a fractional value (e.g. "PT1.5S" -> one "1.5 seconds"
 *   component), since Intl.NumberFormat's "second" unit accepts fractional input.
 * - By default, zero-valued components are omitted (e.g. "P1DT0H30M" -> "1 day, 30
 *   minutes"). Pass { zero: true } to include them.
 * - A zero-length duration (e.g. "PT0S") always renders its seconds component
 *   ("0 seconds") even with the default zero-omitting behavior, since omitting
 *   every component would otherwise produce "".
 * - Negative durations render each component with a leading "-" (Temporal stores
 *   every field of a negative duration as a negative number).
 * - Returns "" for invalid input: non-string value or invalid duration string.
 *
 * @param value ISO 8601 duration string
 * @param locale BCP 47 locale tag, passed to Intl.NumberFormat/Intl.ListFormat; system default if omitted
 * @param options optional: { style: "long" | "short" | "narrow" (default "long"), zero: boolean (default false) }
 * @returns human-readable rendering of the duration, or "" on invalid input
 *
 * @example formatDuration("P1DT2H30M", "en-US") // "1 day, 2 hours, and 30 minutes"
 * @example formatDuration("PT90M", "en-US", { style: "short" }) // "90 min"
 * @example formatDuration("PT90M", "en-US", { style: "narrow" }) // "90m"
 * @example formatDuration("P1DT0H30M", "en-US") // "1 day and 30 minutes"
 * @example formatDuration("PT0S", "en-US") // "0 seconds"
 * @example formatDuration("-P1DT2H", "en-US") // "-1 day and -2 hours"
 * @example formatDuration("P1DT2H30M", "de-DE") // "1 Tag, 2 Stunden und 30 Minuten"
 * @example formatDuration("invalid") // ""
 */
export declare function formatDuration(value: string, locale?: string, options?: FormatDurationOptions): string;