diff -r 0a150985d6b6 -r a4affe75198c ui/ui/toolkit.h
--- a/ui/ui/toolkit.h	Mon May 18 21:29:56 2026 +0200
+++ b/ui/ui/toolkit.h	Tue May 19 18:10:13 2026 +0200
@@ -295,9 +295,10 @@
     UiContainer *container_end;
     
     /*
-     * next container object
+     * called when someone requests to close the window
      */
-    UiObject    *next;
+    void (*onclose)(UiEvent *event, void *userdata);
+    void *onclosedata;
     
     /*
      * obj destroy func