new_contents: class URLButton:
      '''A class representing a URL button.
  
      Attributes:
          text: The text to display on the button.
          url: The url to open when the button is pressed.
  
      '''
      def __init__(self, text, url):
          self.text = text
          self.url = url
  
      def to_json(self):
          '''Converts the button to JSON.
  
          Returns:
              A dictionary holding the JSON representation of the button.
  
          '''
          return {'type': 'web_url',
                  'title': self.text,
                  'url': self.url}
  
subject: Create URL button class