edits

source/tutorial/expire-data.txt

@@ -64,13 +64,13 @@ following command at the :program:`mongo` shell:
 
    db.log.events.ensureIndex( { "status": 1 }, { expireAfterSeconds: 3600 } )
 
-In this example we assume ``status`` holds date/time information.  If in a document in 
-this collection
-the status field is set and is over an hour old, 
-MongoDB will automatically delete the document.
+The ``status`` field *must* hold date/time information. MongoDB will
+automatically delete documents from this collection once the value of
+``status`` is one or more hours old.
 
 Replication
 -----------
 
-The TTL background thread runs on replica set primaries.  Any deletions performed by the thread 
-will replicate to the other members of the set.
+The background TTL thread *only* runs on :term:`primaries <primary>`.
+All deletions operations replicate normally to the other members of
+the set.