code: func RunUse(dockerCli command.Cli, name string) error {
  	if err := validateContextName(name); err != nil && name != "default" {
  		return err
  	}
  	if _, err := dockerCli.ContextStore().GetMetadata(name); err != nil && name != "default" {
  		return err
  	}
  	configValue := name
  	if configValue == "default" {
  		configValue = ""
  	}
  	dockerConfig := dockerCli.ConfigFile()
  	dockerConfig.CurrentContext = configValue
  	if err := dockerConfig.Save(); err != nil {
  		return err
  	}
  	fmt.Fprintln(dockerCli.Out(), name)
  	fmt.Fprintf(dockerCli.Err(), "Current context is now %q\n", name)
  	if os.Getenv("DOCKER_HOST") != "" {
  		fmt.Fprintf(dockerCli.Err(), "Warning: DOCKER_HOST environment variable overrides the active context. "+
  			"To use %q, either set the global --context flag, or unset DOCKER_HOST environment variable.\n", name)
  	}
  	return nil
  }
docs: // RunUse set the current Docker context