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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def format_iso_datetime(datetime_obj):
 """Formats the given datetime as a UTC-zoned ISO 8601 date string. :param datetime_obj: The datetime object. :type datetime_obj: datetime :return: The datetime object in 8601 string form. :rtype: datetime """

    datetime_obj = localize_datetime(datetime_obj, pytz.utc)
    if datetime_obj < MIN_DATE:
        datetime_obj = MIN_DATE
    elif datetime_obj > MAX_DATE:
        datetime_obj = MAX_DATE
    return datetime_obj.replace(tzinfo=None).strftime('%Y-%m-%dT%H:%M:%S.%f')[:-3] + 'Z'