Minor tweak

Author: javiereguiluz

validation/groups.rst

@@ -132,16 +132,18 @@ With this configuration, there are three validation groups:
 
 ``Default``
     Contains the constraints in the current class and all referenced classes
-    that belong to no other group. Contains the constraint on the ``city``
-    field only.
+    that belong to no other group. In this example, it only contains the
+    ``city`` field.
 
 ``User``
     Equivalent to all constraints of the ``User`` object in the ``Default``
     group. This is always the name of the class. The difference between this
     and ``Default`` is explained in :doc:`/validation/sequence_provider`.
 
 ``registration``
-    Contains the constraints on the ``email`` and ``password`` fields only.
+    This is a custom validation group, so it only contains the constraints
+    explicitly associated to it. In this example, only the ``email`` and
+    ``password`` fields.
 
 Constraints in the ``Default`` group of a class are the constraints that have
 either no explicit group configured or that are configured to a group equal to