// Define a custom section.
// The CustomSection type allows to define a custom section 
// programmatically.
public sealed class CustomSection : 
    ConfigurationSection
{
    // The collection (property bag) that contains 
    // the section properties.
    private static ConfigurationPropertyCollection _Properties;
    
    // Internal flag to disable 
    // property setting.
    private static bool _ReadOnly;

    // The FileName property.
    private static readonly ConfigurationProperty _FileName =
        new ConfigurationProperty("fileName", 
        typeof(string),"default.txt", 
        ConfigurationPropertyOptions.IsRequired);

    // The MaxUsers property.
    private static readonly ConfigurationProperty _MaxUsers =
        new ConfigurationProperty("maxUsers", 
        typeof(long), (long)1000, 
        ConfigurationPropertyOptions.None);
    
    // The MaxIdleTime property.
    private static readonly ConfigurationProperty _MaxIdleTime =
        new ConfigurationProperty("maxIdleTime", 
        typeof(TimeSpan), TimeSpan.FromMinutes(5), 
        ConfigurationPropertyOptions.IsRequired);

    // CustomSection constructor.
    public CustomSection()
    {
        // Property initialization
        _Properties = 
            new ConfigurationPropertyCollection();

        _Properties.Add(_FileName);
        _Properties.Add(_MaxUsers);
        _Properties.Add(_MaxIdleTime);
   }

    // This is a key customization. 
    // It returns the initialized property bag.
    protected override ConfigurationPropertyCollection Properties
    {
        get
        {
            return _Properties;
        }
    }

    private new bool IsReadOnly
    {
        get
        {
            return _ReadOnly;
        }
    }

    // Use this to disable property setting.
    private void ThrowIfReadOnly(string propertyName)
    {
        if (IsReadOnly)
            throw new ConfigurationErrorsException(
                "The property " + propertyName + " is read only.");
    }

    // Customizes the use of CustomSection
    // by setting _ReadOnly to false.
    // Remember you must use it along with ThrowIfReadOnly.
    protected override object GetRuntimeObject()
    {
        // To enable property setting just assign true to
        // the following flag.
        _ReadOnly = true;
        return base.GetRuntimeObject();
    }


    [StringValidator(InvalidCharacters = " ~!@#$%^&*()[]{}/;'\"|\\",
        MinLength = 1, MaxLength = 60)]
    public string FileName
    {
        get
        {
            return (string)this["fileName"];
        }
        set
        {
            // With this you disable the setting.
            // Remember that the _ReadOnly flag must
            // be set to true in the GetRuntimeObject.
            ThrowIfReadOnly("FileName");
            this["fileName"] = value;
        }
    }

    [LongValidator(MinValue = 1, MaxValue = 1000000,
        ExcludeRange = false)]
    public long MaxUsers
    {
        get
        {
            return (long)this["maxUsers"];
        }
        set
        {
            this["maxUsers"] = value;
        }
    }

    [TimeSpanValidator(MinValueString = "0:0:30",
        MaxValueString = "5:00:0",
        ExcludeRange = false)]
    public TimeSpan MaxIdleTime
    {
        get
        {
            return  (TimeSpan)this["maxIdleTime"];
        }
        set
        {
            this["maxIdleTime"] = value;
        }
    }
}