code: func (tx *Tx) CreateSpatialIndexOptions(name, pattern string,
  	opts *IndexOptions,
  	rect func(item string) (min, max []float64)) error {
  	return tx.createIndex(name, pattern, nil, rect, nil)
  }
docs: // CreateSpatialIndexOptions is the same as CreateSpatialIndex except that
  // it allows for additional options.