anchor.diff:          member this.ImageSprite with get () = this?ImageSprite () : Sprite
           member this.SetImageSprite (value : Sprite) : Entity = this?ImageSprite <- value
   
  -        // avatar
  -        // uses just block xfields
  -
  -        // tile map
  +        (* avatar xfields *)
  +        // uses same xfields as block
  +
  +        (* tile map xfields *)
           member this.PhysicsIds with get () = this?PhysicsIds () : PhysicsId list
           member this.SetPhysicsIds (value : PhysicsId list) : Entity = this?PhysicsIds <- value
           member this.TileMapAsset with get () = this?TileMapAsset () : TileMapAsset
  
positive.code:                     else (message, true, world)
                  else (message, true, world)
              | _ -> failwith ("Expected MouseButtonData from event '" + addrToStr event + "'.")
      
          let handleButtonEventUpMouseLeft event publisher subscriber message world =
              match message.Data with
              | MouseButtonData (mousePosition, _) ->
  
negative.code:         member this.ToggleSound with get () = this?ToggleSound () : Sound
          member this.SetToggleSound (value : Sound) : Entity = this?ToggleSound <- value
  
          (* feeler xfields *)
          member this.IsTouched with get () = this?IsTouched () : bool
          member this.SetIsTouched (value : bool) : Entity = this?IsTouched <- value
  
          (* block xfields *)
          member this.PhysicsId with get () = this?PhysicsId () : PhysicsId
          member this.SetPhysicsId (value : PhysicsId) : Entity = this?PhysicsId <- value
          member this.Density with get () = this?Density () : single
  