diff --git a/doc/rdoc/markup_reference.rb b/doc/rdoc/markup_reference.rb
index 5b5cdfc706..7622dde0b6 100644
--- a/doc/rdoc/markup_reference.rb
+++ b/doc/rdoc/markup_reference.rb
@@ -859,6 +859,15 @@
# - On-page: DummyClass links to DummyClass.
# - Off-page: RDoc::Alias links to RDoc::Alias.
#
+# Note: For poeple want to mark up code (such as class, module,
+# constant, and method) as "+code+" (for interoperability
+# with other MarkDown parsers mainly), such word that refers a known
+# code object and is marked up entirely and separately as "monofont"
+# is also converted to a link.
+#
+# - +DummyClass+ links to DummyClass
+# - +DummyClass-object+ is not a link.
+#
# [Module]
#
# - On-page: DummyModule links to DummyModule.