docs: def comma_join(fields, oxford=True):
      """ Join together words. """
  
      def fmt(field):
          return "'%s'" % field
  
      if not fields:
          return "nothing"
      elif len(fields) == 1:
          return fmt(fields[0])
      elif len(fields) == 2:
          return " and ".join([fmt(f) for f in fields])
      else:
          result = ", ".join([fmt(f) for f in fields[:-1]])
          if oxford:
              result += ","
          result += " and %s" % fmt(fields[-1])
          return result