--- a/docs/user-guide.rst	Mon Apr 13 15:09:55 2015 -0400
+++ b/docs/user-guide.rst	Mon Apr 13 15:18:01 2015 -0400
@@ -334,7 +334,14 @@
 Obsolete is not hidden
 ======================
 
-TODO
+So far, every obsolete changeset we have seen is also hidden. However,
+these are *not* the same thing—that's why they have different names.
+It's entirely possible to have obsolete changesets that are not
+hidden. We'll see examples of that soon, when we create *unstable*
+changesets.
+
+Note that all hidden changesets are obsolete: hidden is a subset of
+obsolete.
 
 
 Life with ``evolve`` (advanced usage)