document concat as RC

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@556996 13f79535-47bb-0310-9956-ffa450edef68

docs/manual/CoreTypes/resources.html

@@ -318,6 +318,15 @@ Ant's "legacy" datatypes have been modified to behave as Resource Collections:
   </li>
 </ul>
 </p>
+<p>Strangely, some tasks can even legitimately behave as resource collections:
+<ul>
+  <li><a href="../CoreTasks/concat.html">concat</a>
+    exposes a concatenated resource, and adds e.g.
+    <a href="../filterchain.html">filtering</a>
+    to Ant's resource-related capabilities.
+  </li>
+</ul>
+</p>
 <h3>The additional built-in resource collections are:</h3>
 <ul>
   <li><a href="#resources">resources</a> - generic resource collection</li>