code: func label(b *Builder, args []string, attributes map[string]bool, flagArgs []string, original string) error {
  	if len(args) == 0 {
  		return errAtLeastOneArgument("LABEL")
  	}
  	if len(args)%2 != 0 {
  		// should never get here, but just in case
  		return errTooManyArguments("LABEL")
  	}
  
  	if b.RunConfig.Labels == nil {
  		b.RunConfig.Labels = map[string]string{}
  	}
  
  	for j := 0; j < len(args); j++ {
  		// name  ==> args[j]
  		// value ==> args[j+1]
  		b.RunConfig.Labels[args[j]] = args[j+1]
  		j++
  	}
  	return nil
  }
docs: // LABEL some json data describing the image
  //
  // Sets the Label variable foo to bar,
  //