code: func (vars *packageVars) Set(value string) error {
  	// <key>:<value> pair.
  	chunks := strings.SplitN(value, ":", 2)
  	if len(chunks) != 2 {
  		return makeCLIError("expecting <key>:<value> pair, got %q", value)
  	}
  	(*vars)[chunks[0]] = chunks[1]
  	return nil
  }
docs: // Set is called by 'flag' package when parsing command line options.