diff --git a/src/backend/nodes/README b/src/backend/nodes/README
index b3dc9afaf7..d8ae35ce58 100644
--- a/src/backend/nodes/README
+++ b/src/backend/nodes/README
@@ -6,10 +6,30 @@ Node Structures
 Introduction
 ------------
 
+Postgres uses "node" types to organize parse trees, plan trees, and
+executor state trees.  All objects that can appear in such trees must
+be declared as node types.  In addition, a few object types that aren't
+part of parse/plan/execute node trees receive NodeTags anyway for
+identification purposes, usually because they are involved in APIs
+where we want to pass multiple object types through the same pointer.
+
 The node structures are plain old C structures with the first field
 being of type NodeTag.  "Inheritance" is achieved by convention:
 the first field can alternatively be of another node type.
 
+Node types typically have support for being copied by copyObject(),
+compared by equal(), serialized by outNode(), and deserialized by
+nodeRead().  For some classes of Nodes, not all of these support
+functions are required; for example, executor state nodes don't
+presently need any of them.  So far as the system is concerned,
+output and read functions are only needed for node types that can
+appear in parse trees stored in the catalogs.  However, we provide
+output functions for many other node types as well, because they
+are very handy for debugging.
+
+Relevant Files
+--------------
+
 Utility functions for manipulating node structures reside in this
 directory.  Some support functions are automatically generated by the
 gen_node_support.pl script, other functions are maintained manually.
@@ -40,7 +60,7 @@ FILES IN THIS DIRECTORY (src/backend/nodes/)
 
 FILES IN src/include/nodes/
 
-    Node definitions:
+    Node definitions primarily appear in:
 	nodes.h		- define node tags (NodeTag) (*)
 	primnodes.h	- primitive nodes
 	parsenodes.h	- parse tree nodes