code: func (x *Dec) Format(s fmt.State, ch rune) {
  	if ch != 'd' && ch != 'f' && ch != 'v' && ch != 's' {
  		fmt.Fprintf(s, "%%!%c(dec.Dec=%s)", ch, x.String())
  		return
  	}
  	fmt.Fprintf(s, x.String())
  }
docs: // Format is a support routine for fmt.Formatter. It accepts the decimal
  // formats 'd' and 'f', and handles both equivalently.
  // Width, precision, flags and bases 2, 8, 16 are not supported.