code: func parseLabels(spec string, sshConf *service.SSHConfig) error {
  	if spec == "" {
  		return nil
  	}
  	// base syntax parsing, the spec must be in the form of 'key=value,more="better"`
  	lmap, err := client.ParseLabelSpec(spec)
  	if err != nil {
  		return trace.Wrap(err)
  	}
  	if len(lmap) > 0 {
  		sshConf.CmdLabels = make(services.CommandLabels, 0)
  		sshConf.Labels = make(map[string]string, 0)
  	}
  	// see which labels are actually command labels:
  	for key, value := range lmap {
  		cmdLabel, err := isCmdLabelSpec(value)
  		if err != nil {
  			return trace.Wrap(err)
  		}
  		if cmdLabel != nil {
  			sshConf.CmdLabels[key] = cmdLabel
  		} else {
  			sshConf.Labels[key] = value
  		}
  	}
  	return nil
  }
docs: // parseLabels takes the value of --labels flag and tries to correctly populate
  // sshConf.Labels and sshConf.CmdLabels