Index: branches/pyyaml3000/lib/yaml/nodes.py
===================================================================
--- branches/pyyaml3000/lib/yaml/nodes.py	(revision 53)
+++ branches/pyyaml3000/lib/yaml/nodes.py	(revision 55)
@@ -23,5 +23,5 @@
 
 class ScalarNode(Node):
-    pass
+    id = 'scalar'
 
 class CollectionNode(Node):
@@ -29,7 +29,7 @@
 
 class SequenceNode(CollectionNode):
-    pass
+    id = 'sequence'
 
 class MappingNode(CollectionNode):
-    pass
+    id = 'mapping'