[InheritedExport]
   public interface IExtension
   {
       
   }
  
   [AttributeUsage(AttributeTargets.Class)]
   public class ExtensionMetadata : MetadataAttribute
   {
       public ExtensionMetadata(string name) : base(typeof(IExtension))
       {
           this.Name = name;
       }
     
       prop string Name { get; set; }
   }
 
   [ExtensionMetadata("OverridingExtension")]    
   public class OverridingExtension : IExtension
   {
   }