anchor.diff:  
   Messages are sent to both `Widget::update` and `Widget::update_command` to indicate that an event happened. The model can be updated when an event is received.
   
  -Create a `struct` to contain the GTK+ widgets:
  -
  -[source,rust]
  -----
  -struct Widgets {
  -    // …
  -    window: Window,
  -}
  -----
  -
  -Create a `struct` which represents a `Widget` (in this case, the main window of the application):
  +Create a `struct` which represents a `Widget` which contains the GTK+ widgets (in this case, the main window of the application):
   
   [source,rust]
   ----
   struct Win {
  -    widgets: Widgets,
  +    // …
  +    window: Window,
   }
   ----
   
  
positive.code:         match event {
              Quit => gtk::main_quit(),
          }
      }
  
      // The next methods are optional.
  
negative.code: 
      // Return the container of this widget.
      fn container(&self) -> &Self::Container {
          &self.window
      }
  
      // Return the initial model.
      fn model() -> Model {
          Model {
          }
      }
  
      // The model may be updated when a message is received.
  