Don't suggest using a collection name with a dot

source/tutorial/expire-data.txt

@@ -106,26 +106,26 @@ seconds in the ``expireAfterSeconds`` field has passed since the time
 specified in its indexed field. [#field-is-array-of-dates]_
 
 For example, the following operation creates an index on the
-``log.events`` collection's ``createdAt`` field and specifies the
+``log_events`` collection's ``createdAt`` field and specifies the
 ``expireAfterSeconds`` value of ``3600`` to set the expiration time to
 be one hour after the time specified by ``createdAt``.
 
 .. code-block:: javascript
 
-   db.log.events.ensureIndex( { "createdAt": 1 }, { expireAfterSeconds: 3600 } )
+   db.log_events.ensureIndex( { "createdAt": 1 }, { expireAfterSeconds: 3600 } )
 
-When adding documents to the ``log.events`` collection, set the
+When adding documents to the ``log_events`` collection, set the
 ``createdAt`` field to the current time:
 
 .. code-block:: javascript
 
-   db.log.events.insert( {
+   db.log_events.insert( {
       "createdAt": new Date(),
       "logEvent": 2,
       "logMessage": "Success!"
    } )
 
-MongoDB will automatically delete documents from the ``log.events``
+MongoDB will automatically delete documents from the ``log_events``
 collection when the document's ``createdAt`` value
 [#field-is-array-of-dates]_ is older than the number of seconds
 specified in ``expireAfterSeconds``.