DOC #1387 add requested content

base_classes/NXcollection.nxdl.xml

@@ -53,6 +53,17 @@
 		a warning since it is always an optional group.  
 		Anything (groups, fields, or attributes) placed in
 		an :ref:`NXcollection` group will not be validated.
+
+		.. admonition:: NXcollection content is not validated.
+
+		   :ref:`NXcollection` is and will always be for unvalidated content.
+
+		   Any and all content within a :ref:`NXcollection` group specified by
+		   an application definition cannot be validated.
+
+		   It is suggested to use a :ref:`NXparameters` group for similar
+		   content which should be validated.
+
 	</doc>
 
 	<!-- any content is purely optional -->