code: def append(self, png, **options):
  		
  		if not isinstance(png, PNG):
  			raise TypeError("Expect an instance of `PNG` but got `{}`".format(png))
  		control = FrameControl(**options)
  		if control.width is None:
  			control.width = png.width
  		if control.height is None:
  			control.height = png.height
  		self.frames.append((png, control))
docs: Append one frame.
  		
  		:arg PNG png: Append a :class:`PNG` as a frame.
  		:arg dict options: The options for :class:`FrameControl`.