def METHOD_NAME(datetime_string):
    """
    Performs the Date/DateTime Format Check
    Checks if the datetime_string is a valid ISO date or ISO datetime string
    Args:
        datetime_string (str): The date or datetime string
    Returns:
        (dict) An object with the validity of the check and the instance
    """
    return {
        "valid": bool(DatetimeValidator._iso_datetime(datetime_string))
        or bool(DatetimeValidator._iso_date(datetime_string)),
        "value": datetime_string,
    }