anchor.diff:          addHierarchyTreeEntityNode entity form world
           (Cascade, world)
   
  +    let private handleNuGroupRegister (form : GaiaForm) evt world =
  +        refreshGroupTabs form world
  +        refreshHierarchyTreeView form world
  +        (Cascade, world)
  +
  +    let private handleNuGroupUnregistering (form : GaiaForm) evt world =
  +        refreshGroupTabs form world
  +        refreshHierarchyTreeView form world
  +        (Cascade, world)
  +
       let private handleNuEntityRegister (form : GaiaForm) evt world =
           let entity = Entity (atoa evt.Publisher.SimulantAddress)
           addEntityTreeViewNode entity form world
  
positive.code:             let world = updateEditorState (fun editorState -> { editorState with DragCameraState = DragCameraNone }) world
              (Resolve, world)
          | DragCameraNone -> (Resolve, world)
  
      let private monitorEntityEvents (group : Group) form world =
          let world = World.monitor (handleNuChangeParentNodeOpt form) (Events.Change Property? ParentNodeOpt --> group --> Events.Wildcard) group world
  
negative.code:                     | Some _ -> (defaultGroup, world) // NOTE: conclude world is already attached
                  | [] -> failwith ("Cannot attach Gaia to a world with no groups inside the '" + scstring Globals.Screen + "' screen.")
              let world = List.fold (fun world group -> monitorEntityEvents group form world) world groups
              let world = monitorGroupEvents form world
              (defaultGroup, world)
          else failwith ("Cannot attach Gaia to a world with a screen selected other than '" + scstring Globals.Screen + "'.")
  
  