DOCS-13623 Let parameters in aggregate commands

Author: jason-price-mongodb

source/includes/let-variables-example.rst renamed to source/includes/let-constants-example.rst

@@ -13,5 +13,5 @@ The following example:
 - retrieves the cake that has a ``salesTotal`` greater than 3000, which
   is the cake with an ``_id`` of 2
 
-- defines a ``targetTotal`` variable in ``let``, which is referenced in
-  ``$gt`` as ``$$targetTotal``
+- defines a ``targetTotal`` constant in ``let``, which is referenced in
+  ``$gt`` as ``$$targetTotal``

source/includes/let-constants.rst

@@ -0,0 +1,20 @@
+Specifies a document with a list of constants that can be used elsewhere
+in the command. This supports tasks that could otherwise only be
+performed using the :dbcommand:`mapReduce` command, and reduces the risk
+of MQL injection attacks. The document syntax is:
+
+.. code-block:: javascript
+   :copyable: false
+
+   { <constant_name_1>: <value_1>,
+     ...,
+     <constant_name_n>: <value_n> }
+  
+For example: ``{ targetTotal: 3000 }``
+
+Constants must be named according to the :ref:`user variable naming
+conventions<agg-user-variables>`.
+
+To access a constant elsewhere in the command, use the double dollar
+sign prefix (``$$``) together with your constant name in the form
+``$$<constant_name>``. For example: ``$$targetTotal``

source/includes/let-variables.rst

@@ -233,11 +233,15 @@ arguments:
 
      - document
 
-     - Optional.
+     - .. _aggregate-let-option:
 
-       .. include:: /includes/let-variables.rst
+       Optional.
+     
+       .. include:: /includes/let-constants.rst
+
+       For an example, see :ref:`aggregate-let`.
 
-       To view an example, see :ref:`aggregate-let`.
+       .. versionadded:: 5.0
 
 
 .. include:: /includes/deprecation-aggregate-wo-cursor.rst
@@ -547,15 +551,15 @@ majority of the nodes.
 
 .. _aggregate-let:
 
-Use Variables in ``let`` 
+Use Constants in ``let`` 
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
 .. versionadded:: 5.0
 
-To specify variables that can be accessed elswewhere in the command, use
-the :dbcommand:`aggregate` ``let`` option.
+To specify constants that can be accessed elsewhere in the command, use
+the :ref:`let <aggregate-let-option>` option.
 
-.. include:: /includes/let-variables-example.rst
+.. include:: /includes/let-constants-example.rst
 
 .. code-block:: javascript
 

source/reference/command/aggregate.txt

@@ -213,12 +213,15 @@ Definition
 
         - document
 
-        - Optional.
+        - .. _db.collection.aggregate-let-option:
+        
+          Optional.
 
-          .. include:: /includes/let-variables.rst
+          .. include:: /includes/let-constants.rst
 
-          To view an example, see :ref:`db.collection.aggregate-let`.
-          
+          For an example, see :ref:`db.collection.aggregate-let`.
+
+          .. versionadded:: 5.0
 
 
 
@@ -616,15 +619,15 @@ process ID, thread ID, client hostname, and the user who issued the command.
 
 .. _db.collection.aggregate-let:
 
-Use Variables in ``let`` 
+Use Constants in ``let`` 
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
 .. versionadded:: 5.0
 
 To specify variables that can be accessed elsewhere in the command, use
-the :method:`db.collection.aggregate()` ``let`` option.
+the :ref:`let <db.collection.aggregate-let-option>` option.
 
-.. include:: /includes/let-variables-example.rst
+.. include:: /includes/let-constants-example.rst
 
 .. code-block:: javascript
 

source/reference/method/db.collection.aggregate.txt

@@ -21,9 +21,9 @@ General Aggregation Improvements
 ``let``
 ```````
 
-Starting in MongoDB 5.0, :dbcommand:`aggregate` and
-:method:`db.collection.aggregate()` have a ``let`` option to specify a
-list of variables and values that can be used elsewhere in the
+Starting in MongoDB 5.0, the :dbcommand:`aggregate` command and
+:method:`db.collection.aggregate()` helper method have a ``let`` option
+to specify a list of constants that can be used elsewhere in the
 aggregation pipeline. This supports tasks that could otherwise only be
 performed using the :dbcommand:`mapReduce` command, and reduces the risk
 of MQL injection attacks.