anchor.diff:        
   type [<StructuralEquality; NoComparison; CLIMutable>] TileMap =
       { Actor : Actor
  -      //PhysicsIds : Id list
  +      PhysicsIds : Id list
         Density : single
         TileMapAsset : TileMapAsset
         TmxMap : TmxMap
  
positive.code:         let tmxMap = TmxMap "TileMap.tmx"
          TileMap
              { Actor = makeDefaultActor ()
                Density = NormalDensity
                TileMapAsset = { TileMapAssetName = Lun.make "TileMap"; PackageName = Lun.make "Default"; PackageFileName = "AssetGraph.xml" }
                TmxMap = tmxMap
  
negative.code: let entityModelOptActor =
      { Get = fun this ->
          match this with
          | Button _
          | Label _
          | TextBox _
          | Toggle _
          | Feeler _ -> None
          | Block block -> Some block.Actor
          | Avatar avatar -> Some avatar.Actor
          | TileMap tileMap -> Some tileMap.Actor
        Set = fun optActor this ->
          let actor = Option.get optActor
          match this with
          | Button _
          | Label _
          | TextBox _
          | Toggle _
          | Feeler _ -> failwith "EntityModel is not an actor."
          | Block block -> Block { block with Actor = actor }
          | Avatar avatar -> Avatar { avatar with Actor = actor }
          | TileMap tileMap -> TileMap { tileMap with Actor = actor }}
  