/**
 * A utility class for formatting dates using format strings.
 *
 * Supported format specifiers:
 * - `d`   : Day of the month (1-31) without leading zero.
 * - `dd`  : Day of the month (01-31) with leading zero.
 * - `ddd` : Abbreviated name of the day of the week (e.g., Mon, Tue).
 * - `dddd`: Full name of the day of the week (e.g., Monday, Tuesday).
 * - `h`   : Hour (1-12) in 12-hour format without leading zero.
 * - `hh`  : Hour (01-12) in 12-hour format with leading zero.
 * - `H`   : Hour (0-23) in 24-hour format without leading zero.
 * - `HH`  : Hour (00-23) in 24-hour format with leading zero.
 * - `m`   : Minute (0-59) without leading zero.
 * - `mm`  : Minute (00-59) with leading zero.
 * - `M`   : Month (1-12) without leading zero.
 * - `MM`  : Month (01-12) with leading zero.
 * - `MMM` : Abbreviated name of the month (e.g., Jan, Feb).
 * - `MMMM`: Full name of the month (e.g., January, February).
 * - `s`   : Second (0-59) without leading zero.
 * - `ss`  : Second (00-59) with leading zero.
 * - `t`   : First character of the AM/PM designator (e.g., A or P).
 * - `tt`  : Full AM/PM designator (e.g., AM or PM).
 * - `y`   : Year as the last two digits without leading zero (e.g., 9 for 2009).
 * - `yy`  : Year as the last two digits with leading zero (e.g., 09 for 2009).
 * - `yyy` : Year with a minimum of three digits (e.g., 009, 2009).
 * - `yyyy`: Year as a four-digit number (e.g., 2009).
 * - `:`   : Time separator (e.g., colon).
 * - `/`   : Date separator (e.g., slash).
 * - `-`   : Custom separator (e.g., hyphen).
 * - `.`   : Custom separator (e.g., dot).
 *
 * @public
 */
export declare class DateTimeFormatter {
    private static readonly _validSpecifiers;
    private static readonly _formatMapping;
    /**
     * Validates that a format string contains only valid datetime format specifiers.
     *
     * @param format The format string.
     * @returns A validated format string.
     * @throws Error if the format contains invalid specifiers.
     */
    static validateFormat(format: string): string;
    /**
     * Formats a date using a format string.
     *
     * @param date The date to format.
     * @param format The format string.
     * @param locale The locale for Intl formatting (default: 'en-US').
     * @returns The formatted date string.
     */
    static format(date: Date, format: string, locale?: string): string;
}
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