Update master

Author: matulef

draft/core/indexes.txt

@@ -271,8 +271,8 @@ index to locate the document:
 Unique Index
 ~~~~~~~~~~~~
 
-The unique index will cause MongoDB to reject all documents that
-contain a duplicate value for the index field. To create a unique index
+A unique index will cause MongoDB to reject all documents that
+contain a duplicate value for the indexed field. To create a unique index
 on the ``user_id`` field of the ``members`` collection, use the
 following operation in the :program:`mongo` shell:
 
@@ -317,8 +317,9 @@ the :program:`mongo` shell:
 
 .. note::
 
-   Sparse indexes are not `block-level`_ indexes. Think of them as
-   dense indexes with a specific filter.
+   Sparse indexes in MongoDB are not to be confused with `block-level`_ 
+   indexes in other databases. Think of them as dense indexes with a 
+   specific filter.
 
    You can combine the sparse index option with the :ref:`unique
    indexes <index-type-unique>` option so that :program:`mongod` will
@@ -356,7 +357,7 @@ By default, creating an index is a blocking operation. Building an
 index on a large collection of data, the operation can take a long
 time to complete. To resolve this issue, the background option can
 allow you to continue to use your :program:`mongod` instance during
-the index build. Create an index in the background of the ``zipcide``
+the index build. Create an index in the background of the ``zipcode``
 field of the ``people`` collection using a command that resembles the
 following:
 
@@ -417,8 +418,7 @@ construction:
    :dbcommand:`compact` will not run concurrently with a background
    index build.
 
-Queries will not use these indexes until the index build is complete
-because the index builds in the ``system.indexes`` database.
+Queries will not use these indexes until the index build is complete.
 
 .. _index-creation-duplicate-dropping:
 
@@ -540,6 +540,7 @@ data.
 
 .. TODO insert link to special /core/geospatial.txt documentation
    on this topic. once that document exists.
+-- TODO short mention of geoHaystack indexes here?  
 
 Index Limitations
 -----------------
@@ -548,7 +549,7 @@ Be aware of the following current limitations of MongoDB's indexes:
 
 - A collection may have no more than :ref:`64 indexes <limit-number-of-indexes-per-collection>`.
 
-- Indexed items can have no more than :ref:`1024 bytes <limit-index-size>`.
+- Index keys can be no larger than :ref:`1024 bytes <limit-index-size>`.
 
   This includes the field value or values, the field name or names,
   and the :term:`namespace`.