code: func (s *PublicBlockChainAPI) rpcOutputBlock(b *types.Block, inclTx bool, fullTx bool) (map[string]interface{}, error) {
  	fields, err := RPCMarshalBlock(b, inclTx, fullTx)
  	if err != nil {
  		return nil, err
  	}
  	fields["totalDifficulty"] = (*hexutil.Big)(s.b.GetTd(b.Hash()))
  	return fields, err
  }
docs: // rpcOutputBlock uses the generalized output filler, then adds the total difficulty field, which requires
  // a `PublicBlockchainAPI`.