howto/puppet.md

@@ -161,7 +161,13 @@ environment, you can simply use that flag again:
     puppet agent --test --environment test
 
 A node or group of nodes can be switch to a different environment
-using the [external node classifier](#external-node-classifier-enc).
+using the [external node classifier](#external-node-classifier-enc) (ENC), by adding a `environment:`
+key, like this in `nodes/test.torproject.org.yaml`:
+
+    ---
+    environment: test
+    parameters:
+      role: test
 
 Once the feature branch is satisfactory, it can then be merged to
 `production` and deleted: