/**
 * Appends `value` to `str` before trailing whitespaces in `str`.
 * @param str String to append to.
 * @param value String to append.
 * @example
 * const str = 'abc\n\n';
 * const value = 'def';
 * const appended = appendBeforeWhitespaces(str, value); // 'abcdef\n\n'
 */
export declare function appendBeforeWhitespaces(str: string, value: string): string;