/** Where IANA tzdata stops being reference-city best effort. */
export declare const TZDATA_AUTHORITATIVE_FROM_YEAR = 1970;
export interface BirthCoords {
    latitude?: number | null;
    longitude?: number | null;
}
/** True when a naive local datetime needs the server-side historical path. */
export declare function needsHistoricalResolution(dt: string, coords?: BirthCoords): boolean;
/**
 * `localToUtcIso`, but historically correct when it matters.
 *
 * Same contract as `localToUtcIso` (naive value with no `tz` throws the
 * ambiguous-datetime error; zone-suffixed and date-only values pass through).
 * For a pre-1970 naive value with known coordinates, the conversion is done
 * by the API's `/timezone/offset` `datetime_local` mode so the historical
 * correction overlay applies. Everything else — including every post-1970
 * conversion — stays on the local, zero-latency Intl path.
 */
export declare function localToUtcIsoHistorical(field: string, dt: string, tz?: string, coords?: BirthCoords, timezoneField?: string): Promise<string>;