code: func (p *parser) number(val string) float64 {
  	n, err := strconv.ParseInt(val, 0, 64)
  	f := float64(n)
  	if err != nil {
  		f, err = strconv.ParseFloat(val, 64)
  	}
  	if err != nil {
  		p.errorf("error parsing number: %s", err)
  	}
  	return f
  }
docs: // number parses a number.