I have a custom MarkupExtension that simulates binding. It works well in normal assignments but when used in Style Setters, for example:
why don't you
return Value
inside the ProvideValue??
You can bind to only DependencyProperty. make a dependency property for Value in your MyExtension Class!
public static readonly DependencyProperty ValueProperty = DependencyProperty.Register("Value", typeof(Object), typeof(MyContentControl), new UIPropertyMetadata());