minor changes

git-svn-id: https://svn.jboss.org/repos/hibernate/trunk/Hibernate3/doc@5559 1b8cb986-b30d-0410-93ca-fae66ebed9b2

reference/en/modules/collection_mapping.xml

@@ -211,6 +211,9 @@ kittens = cat.getKittens(); // Okay, kittens collection is a Set
             </calloutlist>
         </programlistingco>
 
+        <sect2>
+           <title>Collection foreign keys</title>
+    
             <para>
                 Collection instances are distinguished in the database by the foreign key of
                 the entity that owns the collection. This foreign key is referred to as the
@@ -219,9 +222,6 @@ kittens = cat.getKittens(); // Okay, kittens collection is a Set
                 element. 
             </para>
     
-        <sect2>
-               <title>Collection foreign keys</title>
-    
             <para>
                 There may be a nullability constraint on the foreign key column. For most
                 collections, this is implied. For unidirectional one to many associations,
@@ -237,6 +237,11 @@ kittens = cat.getKittens(); // Okay, kittens collection is a Set
     
             <programlisting><![CDATA[<key column="productSerialNumber" on-delete="cascade"/>]]></programlisting>
             
+            <para>
+                See the previous chapter for a full definition of the <literal>&lt;key&gt;</literal> 
+                element.
+            </para>
+            
         </sect2>
         
         <sect2>
@@ -385,6 +390,7 @@ kittens = cat.getKittens(); // Okay, kittens collection is a Set
         length="N"
         precision="N"
         scale="N"
+        not-null="true|false"
         unique="true|false"
 />]]></programlisting>
             <calloutlist>