docs: def _get_back_up_generator(frame_function, *args, **kwargs):
      """Create a generator for the provided animation function that backs up
      the cursor after a frame. Assumes that the animation function provides
      a generator that yields strings of constant width and height.
  
      Args:
          frame_function: A function that returns a FrameGenerator.
          args: Arguments for frame_function.
          kwargs: Keyword arguments for frame_function.
      Returns:
          a generator that generates backspace/backline characters for
          the animation func generator.
      """
      lines = next(frame_function(*args, **kwargs)).split('\n')
      width = len(lines[0])
      height = len(lines)
      if height == 1:
          return util.BACKSPACE_GEN(width)
      return util.BACKLINE_GEN(height)