code: func (db *DB) Set(envs ...envelope.Envelope) error {
  	return db.db.Update(func(tx *bolt.Tx) error {
  		for _, env := range envs {
  			id := env.GetID()
  
  			b, err := json.Marshal(env)
  			if err != nil {
  				return err
  			}
  
  			bucket, err := tx.CreateBucketIfNotExists([]byte{id.Type()})
  			if err != nil {
  				return err
  			}
  			err = bucket.Put(id[:], b)
  			if err != nil {
  				return err
  			}
  		}
  
  		return nil
  	})
  }
docs: // Set stores the serialized value of env into the db, under key id.
  // Stored values are grouped by their type.