anchor.diff:  
           // track registration
           if registered then
  -            changes.Add (HierarchyAdd (nodeId, entityId))
  +            hierarchyChanges.Add (ComponentAddedToNode (nodeId, entityId))
   
           // register correlation
           if registered && not isolated then
  
positive.code:         member this.IndexSystemHierarchical<'c when 'c : struct and 'c :> 'c Component> () =
              this.IndexSystem<'c, SystemHierarchical<'c, 'w>> ()
  
          member this.IndexTree<'c when 'c : struct and 'c :> 'c Component> () =
              match this.TryIndexSystem<'c, SystemHierarchical<'c, 'w>> () with
              | Some system -> system.Components
              | None -> failwith ("Could not find expected system '" + Unchecked.defaultof<'c>.TypeName + "'.")
  
          member this.PopHierarchyChanges<'c when 'c : struct and 'c :> 'c Component> () =
  
negative.code: 
          // track registration
          if unregistered then
              hierarchyChanges.Add (ComponentAddedToNode (nodeId, entityId))
  
          // unregister correlation
          if unregistered && not isolated then
  