docs: def format_currency_field(__, prec, number, locale):
      """Formats a currency field."""
      locale = Locale.parse(locale)
      currency = get_territory_currencies(locale.territory)[0]
      if prec is None:
          pattern, currency_digits = None, True
      else:
          prec = int(prec)
          pattern = locale.currency_formats['standard']
          pattern = modify_number_pattern(pattern, frac_prec=(prec, prec))
          currency_digits = False
      return format_currency(number, currency, pattern, locale=locale,
                             currency_digits=currency_digits)