diff --git a/lstate.h b/lstate.h
index 32c53a9d..7f9de719 100644
--- a/lstate.h
+++ b/lstate.h
@@ -1,5 +1,5 @@
 /*
-** $Id: lstate.h,v 2.114 2014/07/23 17:15:43 roberto Exp roberto $
+** $Id: lstate.h,v 2.115 2014/08/01 17:33:08 roberto Exp roberto $
 ** Global State
 ** See Copyright Notice in lua.h
 */
@@ -54,7 +54,13 @@ typedef struct stringtable {
 
 
 /*
-** information about a call
+** Information about a call.
+** When a thread yields, 'func' is adjusted to pretend that the
+** top function has only the yielded values in its stack; in that
+** case, the actual 'func' value is saved in field 'extra'. 
+** When a function calls another with a continuation, 'extra' keeps
+** the function index so that, in case of errors, the continuation
+** function can be called with the correct top.
 */
 typedef struct CallInfo {
   StkId func;  /* function index in the stack */