public virtual PeriodsSet GetCopy()
        {
            PeriodsSet result = new PeriodsSet();

            foreach (Period period in periods)
            {
                result.Add(period);
            }
            return(result);
        }
        public static PeriodsSet Parse(string str, IFormatProvider format, char separatorChar)
        {
            PeriodsSet result = new PeriodsSet();

            string[] periodSet = string.Format("{0}", str).Split(separatorChar);
            foreach (string periodStr in periodSet)
            {
                Period dp = Period.Parse(periodStr, format);
                if (dp != null)
                {
                    result.Add(dp);
                }
            }
            return(result);
        }