code: func (idx *TxIndex) TxBlockRegion(hash *chainhash.Hash) (*database.BlockRegion, error) {
  	var region *database.BlockRegion
  	err := idx.db.View(func(dbTx database.Tx) error {
  		var err error
  		region, err = dbFetchTxIndexEntry(dbTx, hash)
  		return err
  	})
  	return region, err
  }
docs: // TxBlockRegion returns the block region for the provided transaction hash
  // from the transaction index.  The block region can in turn be used to load the
  // raw transaction bytes.  When there is no entry for the provided hash, nil
  // will be returned for the both the entry and the error.
  //
  // This function is safe for concurrent access.