anchor.diff:     * The comparison is independent
      * of whether the time is in UTC or in the local time zone.
      *
  -   *     DateTime berlinWallFell = new DateTime(1989, 11, 9);
  -   *     DateTime moonLanding    = DateTime.parse("1969-07-20 20:18:00");
  -   *
  -   *     assert(berlinWallFell.isBefore(moonLanding) == false);
  -   *
  +   * ```
  +   * var now = new DateTime.now();
  +   * var earlier = now.subtract(const Duration(seconds: 5));
  +   * assert(earlier.isBefore(now));
  +   * assert(!now.isBefore(now));
  +   *
  +   * // This relation stays the same, even when changing timezones.
  +   * assert(earlier.isBefore(now.toUtc()));
  +   * assert(earlier.toUtc().isBefore(now));
  +   *
  +   * assert(!now.toUtc().isBefore(now));
  +   * assert(!now.isBefore(now.toUtc()));
  +   * ```
      */
     bool isBefore(DateTime other) {
       return _value < other._value;
  
positive.code: 
  /**
   * An instant in time, such as July 20, 1969, 8:18pm GMT.
   *
   * Create a DateTime object by using one of the constructors
   * or by parsing a correctly formatted string,
  
negative.code:   /**
     * True if this [DateTime] is set to UTC time.
     *
     * ```
     * var dDay = new DateTime.utc(1944, 6, 6);
     * assert(dDay.isUtc);
     * ```
     *
     */
    final bool isUtc;
  