anchor.diff:                      form.propertyGrid.SelectedObject <- entityTds
                       world
                   | _ -> world // don't have an entity address
  -            else world)
  +            else world
   
       let private handleFormCreate atMouse (form : GaiaForm) (_ : EventArgs) =
  -        ignore ^ WorldChangers.Add (fun world ->
  +        addWorldChanger ^ fun world ->
               try let world = pushPastWorld world world
                   let selectedGroup = (World.getUserState world).SelectedGroup
                   let (entity, world) = World.createEntity form.createEntityComboBox.Text None None selectedGroup world
  
positive.code:                         world
                  let world = World.setTickRate 0L world
                  refreshFormOnUndoRedo form world
                  world)
  
      let private handleFormTickingChanged (form : GaiaForm) (_ : EventArgs) =
          ignore ^ WorldChangers.Add (fun world ->
              let tickRate = if form.tickingButton.Checked then 1L else 0L
              let (pastWorld, world) = (world, World.setTickRate tickRate world)
              if tickRate = 1L then pushPastWorld pastWorld world else world)
  
      let private handleFormResetTickTime (_ : GaiaForm) (_ : EventArgs) =
          ignore ^ WorldChangers.Add (fun world ->
              let (pastWorld, world) = (world, World.resetTickTime world)
              pushPastWorld pastWorld world)
  
      let private handleFormCopy (form : GaiaForm) (_ : EventArgs) =
          ignore ^ WorldChangers.Add (fun world ->
              match form.propertyGrid.SelectedObject with
              | null -> world
              | :? EntityTypeDescriptorSource as entityTds -> World.copyToClipboard entityTds.DescribedEntity world; world
              | _ -> Log.trace ^ "Invalid copy operation (likely a code issue in Gaia)."; world)
  
      let private handleFormCut (form : GaiaForm) (_ : EventArgs) =
          ignore ^ WorldChangers.Add (fun world ->
              match form.propertyGrid.SelectedObject with
              | null -> world
              | :? EntityTypeDescriptorSource as entityTds ->
  
negative.code:                         world
                  let world = World.setTickRate 0L world
                  refreshFormOnUndoRedo form world
                  world
  
      let private handleFormRedo (form : GaiaForm) (_ : EventArgs) =
          addWorldChanger ^ fun world ->
              match (World.getUserState world).FutureWorlds with
              | [] -> world
              | futureWorld :: futureWorlds ->
  