DOCS-503 minor style change

Author: Sam Kleinman

source/reference/operator/positional.txt

@@ -10,8 +10,8 @@
 
    The positional :operator:`$` operator identifies an element in an
    ``array`` field to update without explicitly specifying the position
-   of the element in the array. The positional :operator:`$` operator
-   is used in conjunction with the :method:`update()
+   of the element in the array. The positional :operator:`$` operator,
+   when used with the :method:`update()
    <db.collection.update()>` method and acts as a placeholder for the
    **first match** of the update ``query selector``:
 
@@ -69,13 +69,13 @@
    Consider the following behaviors when using the positional
    :operator:`$` operator:
 
-   - The positional :operator:`$` operator should not be used with an
-     :term:`upsert` since an insert will use the ``$`` as a field name
+   - Do not use the positional operator :operator:`$` with
+     :term:`upsert` operations because, inserts will use the ``$`` as a field name
      in the inserted document.
 
    - When used with the :operator:`$unset` operator, the positional
      :operator:`$` operator does not remove the matching element from
-     the array but rather set it to ``null``.
+     the array but rather sets it to ``null``.
 
    .. seealso::