Extend ExpandoObject to control assignment by hooking INotifyPropertyChanged

ExpandoObjectExtensions.cs

public static class Extensions
{
	public static ExpandoObject WithAutoCorrect(this ExpandoObject eo)
	{
		(eo as INotifyPropertyChanged).PropertyChanged += Handler;
		return eo;

		static void Handler(object sender, PropertyChangedEventArgs e)
		{
			var dict = (IDictionary<String, Object>)sender;
			switch (dict[e.PropertyName])
			{
				case String s:
					dict[e.PropertyName] = (ExtendedString)s;
					break;
				case ExtendedString _:
					break;
				default:
					throw new InvalidOperationException($"The value of the property must be of type `{typeof(String).FullName}`.");
			};
		}
	}
}