Simple custom config section with collection in .NET4

Question

I'm trying to write a very simple custom configuration section for a .NET4 application. My goal is this:

<configuration>
  <configSections>
    <section name="myServices" type="My.ConfigSection, My.Assembly" />
  </configSections>
  <myServices>
    <add name="First" />
    <add name="Second" />
  </myServices>
</configuration>

However, I keep getting a ConfigurationErrorsException: 'Unrecognized element 'add'' when I call ConfigurationManager.GetSection("myServices"). I've been staring at it for a while now but haven't figured out yet what I'm doing wrong. Below is my code. It's three classes: ConfigSection, MyServiceSettingsCollection and MyServiceSettings.

First the class that represents the entire config section. It has a nameless default collection of type MyServiceSettingsCollection. The IsDefaultCollection property should allow me to 'add' directly to my collection from the root element.

public sealed class ConfigSection : ConfigurationSection
{
  private static readonly ConfigurationProperty _propMyServices;

  private static readonly ConfigurationPropertyCollection _properties;

  public static ConfigSection Instance { get { return _instance; } }

  static ConfigSection()
  {
    _propMyServices = new ConfigurationProperty(
          null, typeof(MyServiceSettingsCollection), null,
          ConfigurationPropertyOptions.IsDefaultCollection);
    _properties = new ConfigurationPropertyCollection { _propMyServices };
  }

  [ConfigurationProperty("", IsDefaultCollection = true)]
  public MyServiceSettingsCollection MyServices
  {
    get { return (MyServiceSettingsCollection) base[_propMyServices]; }
    set { base[_propMyServices] = value; }
  }

  protected override ConfigurationPropertyCollection Properties
  { get { return _properties; } }
}

Next, the collection class itself. It is of type AddRemoveClearMap.

[ConfigurationCollection(typeof(MyServiceSettings),
    CollectionType = ConfigurationElementCollectionType.AddRemoveClearMap)]
public sealed class MyServiceSettingsCollection : ConfigurationElementCollection
{
  public MyServiceSettings this[int index]
  {
    get { return (MyServiceSettings) BaseGet(index); }
    set
    {
      if (BaseGet(index) != null) { BaseRemoveAt(index); }
      BaseAdd(index, value);
    }
  }

  public new MyServiceSettings this[string key]
  {
    get { return (MyServiceSettings) BaseGet(key); }
  }

  protected override ConfigurationElement CreateNewElement()
  {
    return new MyServiceSettings();
  }

  protected override object GetElementKey(ConfigurationElement element)
  {
    return ((MyServiceSettings) element).Key;
  }
}

And finally a class for the elements in the collection. For now, this class has one property but there will be more later (which prevents me from using NameValueSectionHandler).

public class MyServiceSettings : ConfigurationElement
{
  private static readonly ConfigurationProperty _propName;

  private static readonly ConfigurationPropertyCollection properties;

  static MyServiceSettings()
  {
    _propName = new ConfigurationProperty("name", typeof(string), null, null,
                                          new StringValidator(1),
                                          ConfigurationPropertyOptions.IsRequired |
                                          ConfigurationPropertyOptions.IsKey);
    properties = new ConfigurationPropertyCollection { _propName };
  }

  [ConfigurationProperty("name", DefaultValue = "",
        Options = ConfigurationPropertyOptions.IsRequired |
                  ConfigurationPropertyOptions.IsKey)]
  public string Name
  {
      get { return (string) base[_propKey]; }
      set { base[_propKey] = value; }
  }

  protected override ConfigurationPropertyCollection Properties
  { get { return properties; } }
}

Answer 1

Ok, I found the seemingly random fix. Instead of this:

[ConfigurationProperty("", IsDefaultCollection = true)]
public ProvisiorServiceSettingsCollection ProvisiorServices
{ ... }

you should use:

[ConfigurationProperty("", Options = ConfigurationPropertyOptions.IsDefaultCollection)]
public ProvisiorServiceSettingsCollection ProvisiorServices
{ ... }

No idea what the difference is between the two. To me, they look strikingly similar... or at least, there is no suggestion anywhere why one is preferred over the other.