docs: def save_ds9(output, filename):
      """Save ds9 region output info filename.
  
      Parameters
      ----------
      output : str
          String containing the full output to be exported as a ds9 region
          file.
      filename : str
          Output file name.
  
      """
  
      ds9_file = open(filename, 'wt')
      ds9_file.write(output)
      ds9_file.close()