Per Josh Berkus; some additional explanatory text by me.
<listitem>
<para>
- <emphasis>Implement a truly serializable isolation level</emphasis>
+ <emphasis>Implement Serializable Snapshot Isolation, in order to
+ provide a more robust serializable transaction mode.</emphasis>
+ </para>
+ <para>
+ In previous releases, the REPEATABLE READ and SERIALIZABLE isolation
+ levels were identical. The historical behavior of REPEATABLE READ is
+ unchanged in this release, but SERIALIZABLE now provides stronger
+ guarantees.
</para>
</listitem>