DOCS-11099: tweak wording for key for $geoNear in 4.2

Author: kay-kim

source/includes/apiargs-pipeline-geoNear-field.yaml

@@ -164,16 +164,22 @@ arg_name: field
 interface: pipeline
 operation: geoNear
 description: |
-  Specify the geospatial index to use when calculating the distance.
-  If your collection has multiple geospatial indexes, you **must**
-  use the ``key`` option to specify the indexed field path to use.
-  :ref:`pipeline-geoNear-key-param-example` provides a full example.
+
+   Specify the geospatial indexed field to use when calculating the
+   distance.
+ 
+   If your collection has multiple ``2d`` and/or multiple ``2dsphere``
+   indexes, you **must** use the ``key`` option to specify the indexed
+   field path to use. :ref:`pipeline-geoNear-key-param-example`
+   provides a full example.
+
+   If there is more than one ``2d`` index or more than one ``2dsphere``
+   index and you do not specify a ``key``, MongoDB will return an error.
   
-  If you do not specify the field over which to perform the search with
-  ``key``, MongoDB will attempt to look for a usable ``2d`` or
-  ``2dsphere`` index, in that order. If there is more than one ``2d``
-  index or more than one ``2dsphere`` index, MongoDB will return an
-  error.
+   If you do not specify the ``key``, and you have at most only one
+   ``2d`` index and/or only one ``2dsphere`` index, MongoDB looks first
+   for a ``2d`` index to use. If a ``2d`` index does not exists, then
+   MongoDB looks for a ``2dsphere`` index to use.
 
   .. versionadded:: 4.0
 

source/includes/fact-limitation-one-geo-index-per-collection.rst

@@ -1,14 +1,21 @@
-The :pipeline:`$geoNear` pipeline stage requires that a collection has
-*at most* only one |first-geo-index| and/or only one |second-geo-index|
-whereas :ref:`geospatial query operators <geospatial-query-selectors>`
-(e.g. :query:`$near` and :query:`$geoWithin`) permit collections to
-have multiple geospatial indexes.
-
-The geospatial index restriction for the command and the pipeline stage
-exists because neither the command nor the pipeline stage syntax
-includes the location field. As such, index selection among multiple
-``2d`` indexes or ``2dsphere`` indexes is ambiguous.
-
-No such restriction applies for :ref:`geospatial query operators
-<geospatial-query-selectors>` since these operators take a location
-field, eliminating the ambiguity.
+Starting in MongoDB 4.0, you can specify a ``key`` option to the
+:pipeline:`$geoNear` pipeline stage to indicate the indexed field path
+to use. This allows the :pipeline:`$geoNear` stage to be used on a
+collection that has multiple |first-geo-index| and/or multiple
+|second-geo-index|:
+
+- If your collection has multiple |first-geo-index| and/or multiple
+  |second-geo-index|, you must use the ``key`` option to specify the
+  indexed field path to use.
+
+- If you do not specify the ``key``, you cannot have multiple
+  |first-geo-index| and/or multiple |second-geo-index| since without
+  the ``key``, index selection among multiple ``2d`` indexes or
+  ``2dsphere`` indexes is ambiguous.
+
+.. note::
+
+   If you do not specify the ``key``, and you have at most only one
+   |first-geo-index| index and/or only one |first-geo-index| index,
+   MongoDB looks first for a ``2d`` index to use. If a ``2d`` index
+   does not exists, then MongoDB looks for a ``2dsphere`` index to use.