old_contents: 
  # Some samples.
  
  class Transform(object):
      """Convert a value between Python-native and web-friendly datatypes."""
      
      def __call__(self, value):
          """Get the web-friendly version of this Python-native value."""
          return value
      
      def native(self, value):
          """Get the Python-native version of this web-friendly value."""
          return value
  
  
  class Widget(DataAttribute):
      title = DataAttribute(defualt=None)
      
      transform = DataAttribute(default=Transform())
  
      def decode(self, value):
          return self.default if value is None else self.transform.native(value)
      
      def encode(self, value):
          return self.transform(self.default if value is None else value)
  
  
  class Container(Widget):
      children = DeclarativeAttributes(only=Widget)
      
      def decode(self, value):
          pass
      
      def encode(self, value):
          pass
  
  
  class SampleContainer(Container):
      test = Widget(default=True, title="Testing!")
  
new_contents: 
  # Some samples.
  
  class Transform(object):
      """Convert a value between Python-native and web-friendly datatypes."""
      
      def __call__(self, value):
          """Get the web-friendly version of this Python-native value."""
          return value
      
      def native(self, value):
          """Get the Python-native version of this web-friendly value."""
          return value
  
  
  class Widget(DataAttribute):
      title = DataAttribute(default=None)
      
      transform = DataAttribute(default=Transform())
  
      def decode(self, value):
          return self.default if value is None else self.transform.native(value)
      
      def encode(self, value):
          return self.transform(self.default if value is None else value)
  
  
  class Container(Widget):
      children = DeclarativeAttributes(only=Widget)
      
      def decode(self, value):
          pass
      
      def encode(self, value):
          pass
  
  
  class SampleContainer(Container):
      test = Widget(default=True, title="Testing!")
  
subject: Update widget.py