From ea883f6348d13018179627d5ffd63f22bf843a9f Mon Sep 17 00:00:00 2001
From: Philipp Gesang <phg42.2a@gmail.com>
Date: Tue, 7 May 2013 18:12:54 +0200
Subject: do some basic validation on a node before accepting it as whatsit

---
 luatexbase-attr.dtx | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/luatexbase-attr.dtx b/luatexbase-attr.dtx
index ed60cf7..99b853a 100644
--- a/luatexbase-attr.dtx
+++ b/luatexbase-attr.dtx
@@ -539,7 +539,10 @@ local new_user_whatsit = function (name, package)
     --- unit -> node_t
     local generator = function (proto)
         local res
-        if proto then
+        if  proto
+        and proto.id      == whatsit_t
+        and proto.subtype == user_defined_t
+        then
             local proto_id = proto.user_id
             if proto_id ~= id then --- mismatch
                 warning("overriding user_id %d of whatsit prototype (now: %d)",
-- 
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