code: func (db *DB) schemaIndexPrefix(name string) (id byte, err error) {
  	if name == "" {
  		return 0, errors.New("index name can not be blank")
  	}
  	s, err := db.getSchema()
  	if err != nil {
  		return 0, err
  	}
  	nextID := keyPrefixIndexStart
  	for i, f := range s.Indexes {
  		if i >= nextID {
  			nextID = i + 1
  		}
  		if f.Name == name {
  			return i, nil
  		}
  	}
  	id = nextID
  	s.Indexes[id] = indexSpec{
  		Name: name,
  	}
  	return id, db.putSchema(s)
  }
docs: // schemaIndexID retrieves the complete LevelDB prefix for
  // a particular index.