DOCS-4046ish: Clarify slightly that indexes can be used in either direct...

source/core/indexes-introduction.txt

@@ -63,6 +63,10 @@ directly from the index without requiring an additional sort phase.
 
 .. include:: /images/index-for-sort.rst
 
+An index is traversable for sorting in either direction. For details, see
+:ref:`sorting-with-indexes`.
+
+
 Covered Results
 ~~~~~~~~~~~~~~~
 

source/tutorial/sort-results-with-indexes.txt

@@ -40,6 +40,8 @@ traversing the index in reverse order:
 
    db.records.find().sort( { a: -1 } )
 
+.. _sort-on-multiple-fields:
+
 Sort on Multiple Fields
 -----------------------
 
@@ -100,7 +102,7 @@ memory.
      - ``{ a: 1 }``
 
    * - ``db.data.find().sort( { a: -1 } )``
-   
+
      - ``{ a: 1 }``
 
    * - ``db.data.find().sort( { a: 1, b: 1 } )``
@@ -158,7 +160,7 @@ The following operations can use the index to get the sort order:
      - ``{ a: 1 , b: 1, c: 1 }``
 
    * - ``db.data.find( { b: 3, a: 4 } ).sort( { c: 1 } )``
-   
+
      - ``{ a: 1, b: 1, c: 1 }``
 
    * - ``db.data.find( { a: 5, b: { $lt: 3} } ).sort( { b: 1 } )``