code: func (tg *Group) UnmarshalJSON(b []byte) error {
  	g := struct {
  		Targets []string       `json:"targets"`
  		Labels  model.LabelSet `json:"labels"`
  	}{}
  
  	dec := json.NewDecoder(bytes.NewReader(b))
  	dec.DisallowUnknownFields()
  	if err := dec.Decode(&g); err != nil {
  		return err
  	}
  	tg.Targets = make([]model.LabelSet, 0, len(g.Targets))
  	for _, t := range g.Targets {
  		tg.Targets = append(tg.Targets, model.LabelSet{
  			model.AddressLabel: model.LabelValue(t),
  		})
  	}
  	tg.Labels = g.Labels
  	return nil
  }
docs: // UnmarshalJSON implements the json.Unmarshaler interface.