export interface FormatCalendarOptions {
    reference?: string;
    /**
     * `Intl.DateTimeFormatOptions` `timeStyle` for the time-of-day half.
     * "full" is deliberately not offered here: it appends a `timeZoneName`
     * (e.g. "Coordinated Universal Time"), and plain values have no real
     * timezone — the UTC anchor below is an implementation detail, not a
     * fact about `value`, so surfacing it as a zone name would be a lie.
     */
    timeStyle?: "short" | "medium";
}
/**
 * Format a plain date-time as a relative day label plus time-of-day, e.g.
 * "Tomorrow at 2:30 PM" — Moment's `.calendar()`, which the existing
 * `formatRelativeDateTime` family does not cover (that family renders
 * "in 1 day", an elapsed-time phrase, not a day label + clock time).
 *
 * - Within `±6` days of `reference` (default: now), renders `<day label>`
 *   joined to the localized time using the locale's own connector — never a
 *   hardcoded "at". The day label comes from `Intl.RelativeTimeFormat`
 *   (`numeric: "auto"`), so it reads "Today"/"Tomorrow"/"Yesterday" near
 *   the boundary and "in N days"/"N days ago" further out, all locale-native.
 * - Beyond `±6` days, falls back to an absolute `dateStyle: "long"` +
 *   `timeStyle` string with no relative wording, matching Moment's
 *   `sameElse` behavior.
 * - The connector between the day label and the time is read from CLDR's
 *   own combined date+time pattern for the locale (see
 *   `internal/joinDateTimeConnector.ts`), not hardcoded — this is what lets
 *   `formatCalendar` avoid the i18n objection that excludes a token
 *   formatter (Decision 1 in `context/roadmap/issues/J.md`).
 * - Use `formatCalendar` for user-facing schedules ("Tomorrow at 2:30 PM");
 *   use `formatRelativeDateTime` for elapsed-time displays ("in 1 day").
 *
 * @param value ISO PlainDateTime string to format
 * @param locale optional: BCP 47 locale tag
 * @param options optional: { reference, timeStyle }
 * @returns the formatted calendar string, or "" on invalid input
 *
 * @example formatCalendar("2026-03-16T14:30:00", "en-US", { reference: "2026-03-15T09:00:00" }) // "tomorrow at 2:30 PM"
 * @example formatCalendar("2026-03-08T14:30:00", "en-US", { reference: "2026-03-15T09:00:00" }) // "March 8, 2026 at 2:30 PM" (7 days out — beyond the threshold, absolute fallback)
 * @example formatCalendar("not-a-date") // ""
 */
export declare function formatCalendar(value: string, locale?: string, options?: FormatCalendarOptions): string;