docs: def _get_format_module(image_format):
      """Get the format module to use for optimizing the image."""
      format_module = None
      nag_about_gifs = False
  
      if detect_format.is_format_selected(image_format,
                                          Settings.to_png_formats,
                                          png.PROGRAMS):
          format_module = png
      elif detect_format.is_format_selected(image_format, jpeg.FORMATS,
                                            jpeg.PROGRAMS):
          format_module = jpeg
      elif detect_format.is_format_selected(image_format, gif.FORMATS,
                                            gif.PROGRAMS):
          # this captures still GIFs too if not caught above
          format_module = gif
          nag_about_gifs = True
  
      return format_module, nag_about_gifs