docs: def parse_block(self, block_id, txs):
          """
          Given the sequence of transactions in a block, turn them into a
          sequence of virtual chain operations.
  
          Return the list of successfully-parsed virtualchain transactions
          """
          ops = []
          for i in range(0,len(txs)):
              tx = txs[i]
              op = self.parse_transaction(block_id, tx)
              if op is not None:
                  ops.append( op )
              
          return ops