diff --git a/ROOT b/ROOT
--- a/ROOT
+++ b/ROOT
@@ -1,39 +1,44 @@
 chapter_definition HOL
   description "
     Higher-Order Logic.
 
     Isabelle/HOL is a version of classical higher-order logic resembling
     that of the HOL System (https://www.cl.cam.ac.uk/Research/HVG/HOL).
   "
 
 chapter_definition ZF
   description "
     Zermelo-Fraenkel set theory.
 
     Isabelle/ZF offers a formulation of Zermelo-Fraenkel set theory on top of
     Isabelle/FOL.
   "
 
 chapter_definition FOL
   description "
     First-Order Logic with some variations: single-sorted vs. many-sorted
     (polymorphic), classical vs. intuitionistic, domain-theory (LCF).
   "
 
 chapter_definition Pure
   description "
     The Pure logical framework.
 
     Isabelle/Pure is a version of intuitionistic higher-order logic that
     expresses rules for Natural Deduction declaratively.
   "
 
 chapter_definition Misc
   description "
     Miscellaneous object-logics, tools, and experiments.
   "
 
 chapter_definition Doc
   description "
     Sources of Documentation.
   "
+
+chapter_definition Unsorted
+  description "
+    Sessions without 'chapter' declaration.
+  "