870: Highlights

If you want to define a new widget, then define a subclass of the View class and then define the displayOn: method for that class, by instantiating the following pattern:
```
displayOn: thePen 
  | ... modelValue ... | 
  ... 
  modelValue := self model value. 
  ... 
```
If you want to deploy a widget that you have defined yourself, then define your application model with instance variables to hold an instance of the widget and an instance of a value holder for the widget, and then place a view holder in a canvas, specifying, as the view property of the view holder, an application model getter, and then define that application-model getter such that it produces an instance of the widget, by instantiating the following pattern, in which the selector and instance variable have the same name:
```
selector 
  ^ instance variable isNil 
      ifTrue: [instance variable := widget class new. 
               instance variable model: self a value holder. 
               instance variable] 
      ifFalse: [instance variable] 
```
Whenever a viewer is created, a companion controller is created as well.
If you want to alter the controller used as a viewer companion, then define defaultControllerClass by instantiating the following pattern:
```
defaultControllerClass 
  ^ name of controller class 
```
If you want to define a controller, then define a subclass of the Controller class and implement the controlActivity method for that subclass.