System.Configuration.ConfigurationValues.this C# (CSharp) Метод

        internal object this[string key] {
            get {
                ConfigurationValue configValue = GetConfigValue(key);
                if (configValue != null) {
                    return configValue.Value;
                }
                else {
                    return null;
                }
            }
            set {
                SetValue(key, value, ConfigurationValueFlags.Modified, null);
            }
        }