WhenClass javadoc

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/proxy/branches/version-2.0-work@1515506 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/stub/src/main/java/org/apache/commons/proxy2/stub/BaseTrainer.java b/stub/src/main/java/org/apache/commons/proxy2/stub/BaseTrainer.java
index e9acc30..0a3da5e 100644
--- a/stub/src/main/java/org/apache/commons/proxy2/stub/BaseTrainer.java
+++ b/stub/src/main/java/org/apache/commons/proxy2/stub/BaseTrainer.java
@@ -277,6 +277,11 @@
         }
     }
 
+    /**
+     * Intermediate result of a when(Class) call.
+     * Provided because it is such a common case to have a mismatch between a
+     * declared Class<?> return type and the bound parameter of a class literal.
+     */
     protected class WhenClass extends BaseWhen<Class<?>>
     {
         protected S thenReturn(Class<?> value)