duplicate index behavior backport

Author: rustagir

source/whats-new.txt

@@ -12,26 +12,11 @@ What's New
 
 Learn what's new in:
 
-* :ref:`Version 9.1 <mongoid-version-9.1>`
 * :ref:`Version 9.0 <mongoid-version-9.0>`
 
 To view a list of releases and detailed release notes, see {+odm+}
 :github:`Releases <mongodb/mongoid/releases>` on GitHub.
 
-.. _mongoid-version-9.1:
-
-What's New in 9.1
------------------
-
-The 9.1 release includes the following new features, improvements, and
-fixes:
-
-- Adds the ``Mongoid.allow_duplicate_index_declarations``
-  configuration option that enables you to send index verification to
-  the server. If a duplicate index is declared, the server raises an
-  error. To learn more, see the :ref:`mongoid-config-options-all`
-  section of the Application Configuration guide.
-
 .. _mongoid-version-9.0:
 
 What's New in 9.0
@@ -193,6 +178,15 @@ Removal of Deprecated Functionality
 - The deprecated class ``{+odm+}::Errors::InvalidStorageParent`` has
   been removed.
 
+Index Verification Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+You can use the ``Mongoid.allow_duplicate_index_declarations``
+configuration option to send index verification to
+the server. If a duplicate index is declared, the server raises an
+error. To learn more, see the :ref:`mongoid-config-options-all`
+section of the Application Configuration guide.
+
 ``touch`` Method Clears Changed State
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~