Note that the transaction package is used outside of ZODB

doc/reference/transaction.rst

@@ -3,9 +3,10 @@ Transactions
 ============
 
 Transaction support is provided by the `transaction
-<http://transaction.readthedocs.io/en/latest/>`_ package, which is
-installed automatically when you install ZODB.  There are 2 important
-APIs provided by the transaction package, ``ITransactionManager`` and
+<http://transaction.readthedocs.io/en/latest/>`_ package
+[#transaction-package-can-be-used-wo-ZODB]_, which is installed
+automatically when you install ZODB.  There are two important APIs
+provided by the transaction package, ``ITransactionManager`` and
 ``ITransaction``, described below.
 
 ITransactionManager
@@ -23,3 +24,11 @@ ITransaction
              addBeforeCommitHook, getBeforeCommitHooks,
              addAfterCommitHook, getAfterCommitHooks
 
+
+.. [#transaction-package-can-be-used-wo-ZODB] The :mod:transaction
+   package is a general purpose package for managing `distributed
+   transactions
+   <https://en.wikipedia.org/wiki/Distributed_transaction>`_ with a
+   `two-phase commit protocol
+   <https://en.wikipedia.org/wiki/Two-phase_commit_protocol>`_.  It
+   can and occasionally is used with packages other than ZODB.