SERVER-6335 aggreation: no operations in statements

Author: Sam Kleinman

source/reference/aggregation.txt

@@ -284,6 +284,11 @@ The current pipeline operators are:
       advantage of :term:`indexes <index>` like any other
       :mongodb:func:`db.collection.find()` or :mongodb:func:`db.collection.findOne()`.
 
+   .. warning::
+
+      You cannot use :mongodb:operator:`$where` operations in
+      :pipeline:`$match` queries as part of the aggregation pipeline.
+
 .. pipeline:: $limit
 
    Restricts the number of :term:`documents <document>` that