anchor.diff:          | (true, system) -> system.Correlateds
           | (false, _) -> failwith ("Member with id '" + scstring memberId + "' not found.")
   
  -    member this.AddMember (parentIdOpt : Guid option) =
  +    member this.AddMember (ancestorIdOpt : Guid option) =
           let memberId = Gen.id
           let system = SystemCorrelated<'c, 'w> (buffered, true, ecs)
           let addedOpt =
  -            match parentIdOpt with
  -            | Some parentId ->
  -                let parentIdStr = string parentId
  -                systemTree |> ListTree.tryInsert (fun system -> system.Name = parentIdStr) system
  +            match ancestorIdOpt with
  +            | Some ancestorId ->
  +                let ancestorIdStr = string ancestorId
  +                systemTree |> ListTree.tryInsert (fun system -> system.Name = ancestorIdStr) system
               | None ->
                   systemTree |> ListTree.tryAdd tautology system
           if Option.isSome addedOpt then
  -            familyChanges.Add { FamilyChangeType = MemberAdded; MemberId = memberId; ParentIdOpt = match parentIdOpt with Some pid -> pid | None -> Guid.Empty }
  +            familyChanges.Add { FamilyChangeType = MemberAdded; MemberId = memberId; AncestorIdOpt = match ancestorIdOpt with Some pid -> pid | None -> Guid.Empty }
               systemDict.Add (memberId, system)
               Some memberId
           else None
  
positive.code:         Seq.iter (fun system ->
              system.EntitiesCorrelated |>
              Seq.iter (fun correlated ->
                  familyChanges.Add { FamilyChangeType = ComponentRemovedFromMember; MemberId = memberId; ParentIdOpt = correlated }
                  system.UnregisterCorrelated correlated |> ignore<bool>))
  
          // remove member's system from tree
  
negative.code: 
          // track registration
          if registered then
              familyChanges.Add { FamilyChangeType = ComponentAddedToMember; MemberId = memberId; AncestorIdOpt = entityId }
  
          // register correlation
          if registered && not isolated then
  