code: func ValidateSpec(spec SysSpec, runtime string) (error, error) {
  	// OS-level validators.
  	var osValidators = []Validator{
  		&OSValidator{Reporter: DefaultReporter},
  		&KernelValidator{Reporter: DefaultReporter},
  		&CgroupsValidator{Reporter: DefaultReporter},
  		&packageValidator{reporter: DefaultReporter},
  	}
  	// Docker-specific validators.
  	var dockerValidators = []Validator{
  		&DockerValidator{Reporter: DefaultReporter},
  	}
  
  	validators := osValidators
  	switch runtime {
  	case "docker":
  		validators = append(validators, dockerValidators...)
  	}
  	return Validate(spec, validators)
  }
docs: // ValidateSpec uses all default validators to validate the system and writes to stdout.