DOCS-15300 Add lookup and unionwith (#1306)

* DOCS-15300 Add lookup and unionwith

* DOCSP-15300 updates for feedback

* DOCSP-15300 included searchMeta restrictions

Author: kanchana-mongodb

source/reference/operator/aggregation/lookup.txt

@@ -410,33 +410,70 @@ the ``pipeline`` field.
 Atlas Search Support 
 ~~~~~~~~~~~~~~~~~~~~
 
-Starting in v6.0, the ``pipeline`` can contain the :atlas:`Atlas Search 
-</atlas-search>` :pipeline:`$search` stage as the first stage inside 
-the pipeline. 
+Starting in MongoDB 6.0, you can specify the :atlas:`Atlas Search 
+</atlas-search>` :pipeline:`$search` or :pipeline:`$searchMeta` stage 
+in the ``$lookup`` pipeline to search collections on the Atlas 
+cluster. The :pipeline:`$search` or the :pipeline:`$searchMeta` stage 
+must be the first stage inside the ``$lookup`` pipeline.
 
 For example, when you :ref:`lookup-syntax-let-pipeline` or run 
 :ref:`lookup-syntax-concise-correlated-subquery`, you can specify 
-:pipeline:`$search` inside the pipeline as shown below:
-
-.. code-block:: 
-   :copyable: false 
-   :emphasize-lines: 7-11
-
-   [{
-     "$lookup": {
-       "from": <joined collection>,
-       "let": {<var_n>: <expression>, ...},
-       "as": <output array field>,
-       "pipeline": [{
-         "$search": {
-           "<operator>": {
-             <operator-specification>
+:pipeline:`$search` or :pipeline:`$searchMeta` inside the pipeline as 
+shown below:
+
+.. tabs:: 
+
+   .. tab:: $search
+      :tabid: search
+
+      .. code-block:: 
+         :copyable: false 
+         :emphasize-lines: 7-11
+
+         [{
+           "$lookup": {
+             "from": <joined collection>,
+             localField: <field from the input documents>,
+             foreignField: <field from the documents of the "from" collection>,
+             "as": <output array field>,
+             "pipeline": [{
+               "$search": {
+                 "<operator>": {
+                   <operator-specification>
+                 }
+               },
+               ... 
+             }]
            }
-         },
-         ... 
-       }]
-     }
-   }] 
+         }] 
+
+   .. tab:: $searchMeta
+      :tabid: searchmeta
+
+      .. code-block:: 
+         :copyable: false 
+         :emphasize-lines: 7-11
+
+         [{
+           "$lookup": {
+             "from": <joined collection>,
+             localField: <field from the input documents>,
+             foreignField: <field from the documents of the "from" collection>,
+             "as": <output array field>,
+             "pipeline": [{
+               "$searchMeta": {
+                 "<collector>": {
+                   <collector-specification>
+                 }
+               },
+               ... 
+             }]
+           }
+         }] 
+
+To see an example of :pipeline:`$lookup` with :pipeline:`$search`, 
+see the Atlas Search tutorial :atlas:`Run an Atlas Search $search Query 
+Using $lookup </atlas-search/tutorial/lookup-with-search/>`.
 
 .. _lookup-sharded-collections:
 

source/reference/operator/aggregation/unionWith.txt

@@ -212,27 +212,59 @@ top-level collection/view on which the
 Atlas Search Support
 ~~~~~~~~~~~~~~~~~~~~
 
-Starting in v6.0, the ``pipeline`` can contain the :atlas:`Atlas Search 
-</atlas-search>` :pipeline:`$search` stage as the first stage inside 
-the pipeline.
-
-.. code-block:: 
-   :copyable: false 
-   :emphasize-lines: 5-9
-
-   [{
-     "$unionWith": {
-       "coll": <collection-name>,
-       "pipeline": [{
-         "$search": {
-           "<operator>": {
-             <operator-specification>
+Starting in MongoDB 6.0, you can specify the :atlas:`Atlas Search 
+</atlas-search>` :pipeline:`$search` or :pipeline:`$searchMeta` stage 
+in the ``$unionWith`` pipeline to search collections on the Atlas 
+cluster. The :pipeline:`$search` or the :pipeline:`$searchMeta` stage 
+must be the first stage inside the ``$unionWith`` pipeline. 
+
+.. tabs:: 
+
+   .. tab:: $search
+      :tabid: search
+
+      .. code-block:: 
+         :copyable: false 
+         :emphasize-lines: 5-9
+
+         [{
+           "$unionWith": {
+             "coll": <collection-name>,
+             "pipeline": [{
+               "$search": {
+                 "<operator>": {
+                   <operator-specification>
+                 }
+               },
+               ... 
+             }]
            }
-         },
-         ... 
-       }]
-     }
-   }] 
+         }] 
+
+   .. tab:: $searchMeta
+      :tabid: searchmeta
+
+      .. code-block:: 
+         :copyable: false 
+         :emphasize-lines: 5-9
+
+         [{
+           "$unionWith": {
+             "coll": <collection-name>,
+             "pipeline": [{
+               "$searchMeta": {
+                 "<collector>": {
+                   <collector-specification>
+                 }
+               },
+               ...
+             }]
+           }
+         }] 
+
+To see an example of :pipeline:`$unionWith` with :pipeline:`$search`, 
+see the Atlas Search tutorial :atlas:`Run an Atlas Search $search Query 
+Using $unionWith </atlas-search/tutorial/search-with-unionwith/>`.
 
 Restrictions
 ~~~~~~~~~~~~