diff --git a/doc/src/sgml/pageinspect.sgml b/doc/src/sgml/pageinspect.sgml
index 6f51dc6..433bcb2 100644
--- a/doc/src/sgml/pageinspect.sgml
+++ b/doc/src/sgml/pageinspect.sgml
@@ -192,6 +192,13 @@ test=# SELECT * FROM bt_page_items('pg_cast_oid_index', 1);
           7 | (0,7)   |      12 | f     | f    | 29 27 00 00
           8 | (0,8)   |      12 | f     | f    | 2a 27 00 00
 </screen>
+      Note that <structfield>ctid</> addresses a heap tuple if the
+      page under consideration is a B-Tree leaf page.  Otherwise, for
+      internal B-Tree pages <structfield>ctid</> addresses a page in
+      the B-Tree itself (excluding the root page if and only if there
+      has not yet been a root page split, as in the example above).
+      These internally referenced pages are child pages, and may
+      themselves be leaf pages or internal pages.
      </para>
     </listitem>
    </varlistentry>