Mention pickle protocol 4, and some tweaks.
diff --git a/Doc/library/pickle.rst b/Doc/library/pickle.rst
index cfd5f79..1f35b60 100644
--- a/Doc/library/pickle.rst
+++ b/Doc/library/pickle.rst
@@ -94,6 +94,9 @@
The :mod:`json` module: a standard library module allowing JSON
serialization and deserialization.
+
+.. _pickle-protocols:
+
Data stream format
------------------
@@ -125,10 +128,15 @@
efficient pickling of :term:`new-style class`\es. Refer to :pep:`307` for
information about improvements brought by protocol 2.
-* Protocol version 3 was added in Python 3. It has explicit support for
+* Protocol version 3 was added in Python 3.0. It has explicit support for
:class:`bytes` objects and cannot be unpickled by Python 2.x. This is
- the default as well as the current recommended protocol; use it whenever
- possible.
+ the default protocol, and the recommended protocol when compatibility with
+ other Python 3 versions is required.
+
+* Protocol version 4 was added in Python 3.4. It adds support for very large
+ objects, pickling more kinds of objects, and some data format
+ optimizations. Refer to :pep:`3154` for information about improvements
+ brought by protocol 4.
.. note::
Serialization is a more primitive notion than persistence; although
@@ -156,13 +164,16 @@
.. data:: HIGHEST_PROTOCOL
- The highest protocol version available. This value can be passed as a
- *protocol* value.
+ An integer, the highest :ref:`protocol version <pickle-protocols>`
+ available. This value can be passed as a *protocol* value to functions
+ :func:`dump` and :func:`dumps` as well as the :class:`Pickler`
+ constructor.
.. data:: DEFAULT_PROTOCOL
- The default protocol used for pickling. May be less than HIGHEST_PROTOCOL.
- Currently the default protocol is 3, a new protocol designed for Python 3.0.
+ An integer, the default :ref:`protocol version <pickle-protocols>` used
+ for pickling. May be less than :data:`HIGHEST_PROTOCOL`. Currently the
+ default protocol is 3, a new protocol designed for Python 3.0.
The :mod:`pickle` module provides the following functions to make the pickling