code: func (c *SDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
  	*c = DefaultSDConfig
  	type plain SDConfig
  	err := unmarshal((*plain)(c))
  	if err != nil {
  		return err
  	}
  	if c.Role == "" {
  		return errors.New("role missing (one of: instance, hypervisor)")
  	}
  	if c.Region == "" {
  		return errors.New("openstack SD configuration requires a region")
  	}
  	return nil
  }
docs: // UnmarshalYAML implements the yaml.Unmarshaler interface.