How an internal class in Server.dll can be use in Client.dll???

[Kim]

How an internal class in Server.dll can be use in Client.dll???

When i read the System.Workflow .Runtime.dll's source, I found the
following code is difficult to understand.

public void SubscribeForCor relationTokenIn itializedEvent( Activity
activity, IActivityEventL istener<Correla tionTokenEventA rgs>
dataChangeListe ner)
{
if (null == activity)
{
throw new ArgumentNullExc eption("activit y");
}
if (null ==dataChangeLis tener)
{
throw new ArgumentNullExc eption("dataCha ngeListener");
}

ActivityExecuto rDelegateInfo<C orrelationToken EventArgs>
item = new
ActivityExecuto rDelegateInfo<C orrelationToken EventArgs>(data ChangeListener,
ContextActivity Utils.ContextAc tivity(activity ), true);

IList<ActivityE xecutorDelegate Info<Correlatio nTokenEventArgs >list =
base.GetValue(S ubscriptionsPro perty) as
IList<ActivityE xecutorDelegate Info<Correlatio nTokenEventArgs >>;
if (list == null)
{
list = new
List<ActivityEx ecutorDelegateI nfo<Correlation TokenEventArgs> >();
base.SetValue(S ubscriptionsPro perty, list);
}
list.Add(item);
}

that is a method of class CorrelationToke n in
System.Workflow .Runtime.dll, But ActivityExecuto rDelegateInfo<T is
an interal class in System.Workflow .ConponentModel .dll!!!
how and why?