anchor.diff:  
   type [<TypeDescriptionProvider (typeof<EntityModelTypeDescriptorProvider>)>] EntityModelTypeDescriptorSource =
       { Address : Address
  +      WorldChangers : WorldChangers
         RefWorld : World ref }
   
   and EntityModelPropertyDescriptor (property : PropertyInfo) =
  
positive.code:         world_
      | DragRotation (pickOffset, origPosition, address) -> world_
  
  let createNuEditForm refWorld =
      
      let form = new NuEditForm ()
      form.displayPanel.MaximumSize <- Drawing.Size (ScreenWidth, ScreenHeight)
  
negative.code: let DefaultRotation = 0.0f
  let (ScreenWidth, ScreenHeight) = (900, 600)
  
  type WorldChanger = World -> World
  type WorldChangers = WorldChanger List
  
  type DragState =
      | DragNone
  