anchor.diff:  %% @doc
   %% Abort a transaction.
   %%
  +%% This function causes an abnormal termination of the transaction. The
  +%% log is played backward, and any necessary undo operations are
  +%% performed. Before this function returns, any locks held by the
  +%% transaction will have been released.
  +%%
  +%% In the case of nested transactions, aborting a parent transaction
  +%% causes all children (unresolved or not) of the parent transaction to
  +%% be aborted.
  +%%
  +%% All cursors opened within the transaction must be closed before the
  +%% transaction is aborted.
  +%%
   %% @spec txn_abort() -> ok | {error, Error}
   %%
   %% @end
  
positive.code: 
  %%--------------------------------------------------------------------
  %% @doc
  %% Commit a transaction.
  %%
  %% @spec txn_commit() -> ok | {error, Error}
  %%
  
negative.code: 
  %%--------------------------------------------------------------------
  %% @doc
  %% Store a value in a database file raising an exception on failure.
  %%
  %% This function is the same as put/4 except that it raises an exception
  %% on failure instead of returning an error tuple.
  %%
  %% @see put/4
  %%
  %% @spec put_r(Db, Key, Value, Opts) -> ok
  %% where
  