Index: library/lib/nx-callback.add
===================================================================
diff -u
--- library/lib/nx-callback.add	(revision 0)
+++ library/lib/nx-callback.add	(revision 8a1a24217e47f9201373a60162da255f6649d0b4)
@@ -0,0 +1,4 @@
+# -*- Tcl -*-
+namespace eval ::nsf {
+  set traitIndex(nx::traits::callback) {script {package require nx::traits::callback}}
+}