code: func (a *Action) UnmarshalYAML(unmarshal func(interface{}) error) error {
  	var s string
  	if err := unmarshal(&s); err != nil {
  		return err
  	}
  	switch act := Action(strings.ToLower(s)); act {
  	case Replace, Keep, Drop, HashMod, LabelMap, LabelDrop, LabelKeep:
  		*a = act
  		return nil
  	}
  	return errors.Errorf("unknown relabel action %q", s)
  }
docs: // UnmarshalYAML implements the yaml.Unmarshaler interface.