System.Configuration.CommaDelimitedStringCollection.this C# (CSharp) Method

        public new string this[int index] {
            get {
                return (string)base[index];
            }
            set {
                ThrowIfReadOnly();
                ThrowIfContainsDelimiter(value);
                _Modified = true;
                base[index] = value.Trim();
            }
        }