DOCS-362 correcting capped collections _id index

Author: Sam Kleinman

source/core/indexes.txt

@@ -91,18 +91,10 @@ is a 12-byte unique identifiers suitable for use as the value of an
    *not* print ``unique: true`` in the :program:`mongo` shell.
 
 .. [#capped-collections] Before version 2.2 capped collections did not
-   have an ``_id`` field by default. In 2.2, all capped collections
-   have an ``_id`` field, except those in the ``local``
-   :term:`database`. See the :ref:`release notes
-   <2.2-id-indexes-capped-collections>` for more
-   information.
-
-   Additionally, MongoDB does not create indexes on capped collections
-   by default do not have an index on the ``_id`` field.  In the
-   course of replicating a capped collection, :term:`secondary`
-   members of the set will create an ``_id`` index. If you specify
-   ``autoIndexId: true`` when creating a capped collection MongoDB
-   will create an ``_id`` index on this collection.
+   have an ``_id`` field. In 2.2, all capped collections
+   have an ``_id`` field, except those in the ``local`` :term:`database`.
+   See the :ref:`release notes <2.2-id-indexes-capped-collections>`
+   for more information.
 
 .. TODO fix the above when a full capped-collection page exists.
 

source/release-notes/2.2.txt

@@ -384,21 +384,14 @@ use and state. In previous versions, these data were sampled. See
 
 .. _2.2-id-indexes-capped-collections:
 
-``_id`` Indexes on Capped Collections
-`````````````````````````````````````
+``_id`` Fields and Indexes on Capped Collections
+````````````````````````````````````````````````
 
 All :term:`capped collections <capped collection>` now have an ``_id``
-field by default if they exist outside of the ``local`` database. This
-change only affects capped collections created with 2.2 instances and
-does not impact existing capped collections.
-
-Additionally in :term:`replica sets <replica set>`, :term:`secondaries
-<secondary>` will create indexes on the ``_id`` field for capped
-collections.
-
-By requiring an ``_id`` field, and creating ``_id`` indexes on
-secondaries, MongoDB prevents situations where the absence of an
-``_id`` field can cause problems for replication.
+field by default *if* they exist outside of the ``local`` database,
+and indexes on the ``_id`` field. This change only affects capped
+collections created with 2.2 instances and does not impact existing
+capped collections.
 
 See: :issue:`SERVER-5516` for more information.