diff --git a/util.ml b/util.ml
index c5227e4270111168884fdfff1303b2348e8286aa..ca8d168758c4cc1dad8becb29a6a37b69ef2260c 100644
--- a/util.ml
+++ b/util.ml
@@ -95,6 +95,8 @@ let prerr_loc_msg verbose loc msg =
         with Sys_error _ -> ()
   end
 
+(** AST traversal *)
+
 #define TRAV_ALL(id, constructor) \
   trav_all_##id l = \
     let rec filter_clear = function \