old_contents: class Backend(object):
      """
      Manhattan backend superclass.
  
      A subclass should implement at least the following methods:
  
          record_page
  
          record_pixel
  
          record_goal
  
          record_split
      """
      pass
  
new_contents: class Backend(object):
      """
      Manhattan backend superclass.
  
      A subclass should implement at least the following method, where ``record``
      is an instance of manhattan.record.Record.
  
          def handle(self, record):
              pass
  
      """
      pass
  
subject: update base Backend docstring