DOCS-617 edits

Author: kay-kim

draft/core/write-operations.txt

@@ -285,14 +285,14 @@ Isolation
 ---------
 
 When a single write operation modifies multiple documents, the
-operation as a whole is not atomic, but the modification of each
-document is. The modification of a single Mongo document (or record)
-remains atomic even if the write operation modifies more than one
-sub-document *within* that document.
+operation as a whole is not atomic, and other operations may
+interleave. The modification of a single document, or record, is always
+atomic, even if the write operation modifies multiple sub-document
+*within* the single record.
 
 No other operations are atomic; however, you can attempt to isolate a
-write operation that affects multiple documents using the :doc:`$atomic
-isolation operator </reference/operator/atomic>`.
+write operation that affects multiple documents using the
+:doc:`isolation operator </reference/operator/atomic>`.
 
 To isolate a sequence of write operations from other read and write
 operations, see :doc:`/tutorial/perform-two-phase-commits`.