code: func (qf qFlag) Set(val string) error {
  	q, err := ParseQuantity(val)
  	if err != nil {
  		return err
  	}
  	// This copy is OK because q will not be referenced again.
  	*qf.dest = *q
  	return nil
  }
docs: // Sets the value of the internal Quantity. (used by flag & pflag)