DOCS-662 restrictions on doc field names

Author: kay-kim

draft/applications/create.txt

@@ -33,6 +33,8 @@ MongoDB v2.2 has a 16 megabytes limit on document size.
 
 .. include:: /includes/note-write-concerns.rst
 
+.. include:: /includes/warning-document-field-name-restrictions.rst
+
 .. _crud-create-insert:
 
 Insert

draft/core/documents.txt

@@ -29,6 +29,8 @@ documents may contain ``field:value`` pairs where the value can be
 another document, an array, an array of documents as well as the basic
 types such as ``Double``, ``String``, or ``Date``.
 
+.. include:: /includes/warning-document-field-name-restrictions.rst
+
 Consider the following examples of MongoDB documents:
 
 - The following document specifies a record in a collection. Documents

source/includes/warning-document-field-name-restrictions.rst

@@ -0,0 +1,8 @@
+.. warning::
+
+   :doc:`core/documents` stored as records in collections have
+   the following restrictions on the field names:
+   
+   - The field names must **not** start with the ``$`` character.
+   
+   - The field names must **not** contain the ``.`` character.