Index: generic/nsf.c
===================================================================
diff -u -N -r7ca41c65294c91734558ea49037af2e5ff362e8a -rdadf28efd0707ae40076f49837e6b45ad5b2a989
--- generic/nsf.c	(.../nsf.c)	(revision 7ca41c65294c91734558ea49037af2e5ff362e8a)
+++ generic/nsf.c	(.../nsf.c)	(revision dadf28efd0707ae40076f49837e6b45ad5b2a989)
@@ -403,7 +403,7 @@
   nonnull(1) returns_nonnull;
 
 /* misc prototypes */
-static int SetInstVar(Tcl_Interp *interp, NsfObject *object, Tcl_Obj *nameObj, Tcl_Obj *valueObj)
+static int SetInstVar(Tcl_Interp *interp, NsfObject *object, Tcl_Obj *nameObj, Tcl_Obj *valueObj, unsigned int flags)
   nonnull(1) nonnull(2) nonnull(3);
 
 static int ListDefinedMethods(Tcl_Interp *interp, NsfObject *object, const char *pattern,
@@ -515,7 +515,7 @@
   Tcl_InterpState  state;
   NsfRuntimeState *rst;
   int              result, prevDoProfile;
-  unsigned int     prevPreventRecursionFlags;
+  unsigned int     prevPreventRecursionFlags = 0u;
 
   nonnull_assert(interp != NULL);
   nonnull_assert(dsPtr != NULL);
@@ -9053,11 +9053,13 @@
   nonnull_assert(cmdListPtr != NULL);
 
   if (cmd != NULL) {
-    for (; likely(cmdListPtr != NULL); cmdListPtr = cmdListPtr->nextPtr) {
+    do {
       if (cmdListPtr->cmdPtr == cmd) {
         return cmdListPtr->nextPtr;
       }
-    }
+      cmdListPtr = cmdListPtr->nextPtr;
+    } while  likely(cmdListPtr != NULL);
+
     return NULL;
   }
   return cmdListPtr;
@@ -13339,7 +13341,7 @@
    * Resetting mixin and filter stacks
    */
 
-  if (unlikely((flags & NSF_CSC_MIXIN_STACK_PUSHED) && object->mixinStack) != 0u) {
+  if (unlikely((flags & NSF_CSC_MIXIN_STACK_PUSHED) && object->mixinStack != NULL) != 0u) {
     /* fprintf(stderr, "MixinStackPop %s.%s %p %s\n",
        ObjectName(object), methodName, object->mixinStack, msg);*/
     MixinStackPop(object);
@@ -17482,7 +17484,7 @@
   }
   if (cscPtr->frameType == NSF_CSC_TYPE_ACTIVE_FILTER) {
     methodName = MethodName(cscPtr->filterStackEntry->calledProc);
-  } else if (cscPtr->frameType == NSF_CSC_TYPE_ACTIVE_MIXIN && object->mixinStack) {
+  } else if (cscPtr->frameType == NSF_CSC_TYPE_ACTIVE_MIXIN && object->mixinStack != NULL) {
     methodName = Tcl_GetCommandName(interp, cscPtr->cmdPtr);
   } else {
     return NULL;
@@ -17554,7 +17556,7 @@
   }
 
   if ((objflags & NSF_FILTER_ORDER_VALID) != 0u
-      && object->filterStack
+      && (object->filterStack != NULL)
       && object->filterStack->currentCmdPtr) {
     *cmdPtr = FilterSearchProc(interp, object, currentCmdPtr, clPtr);
 
@@ -18719,11 +18721,11 @@
 #endif
   CleanupDestroyObject(interp, object, 0);
 
-  while (object->mixinStack) {
+  while (object->mixinStack != NULL) {
     MixinStackPop(object);
   }
 
-  while (object->filterStack) {
+  while (object->filterStack != NULL) {
     FilterStackPop(object);
   }
 
@@ -20045,30 +20047,67 @@
  *----------------------------------------------------------------------
  */
 static int
-SetInstVar(Tcl_Interp *interp, NsfObject *object, Tcl_Obj *nameObj, Tcl_Obj *valueObj) {
+SetInstVar(Tcl_Interp *interp, NsfObject *object, Tcl_Obj *nameObj, Tcl_Obj *valueObj, unsigned int flags) {
   CallFrame frame, *framePtr = &frame;
   Tcl_Obj *resultObj;
-  unsigned int flags;
 
   nonnull_assert(interp != NULL);
   nonnull_assert(object != NULL);
   nonnull_assert(nameObj != NULL);
 
-  flags = (object->nsPtr) ? TCL_LEAVE_ERR_MSG|TCL_NAMESPACE_ONLY : TCL_LEAVE_ERR_MSG;
   Nsf_PushFrameObj(interp, object, framePtr);
 
-  if (likely(valueObj == NULL)) {
-    resultObj = Tcl_ObjGetVar2(interp, nameObj, NULL, flags);
+  if ((flags & NSF_VAR_TRIGGER_TRACE) != 0u) {
+    int tclVarFlags;
+    /*
+     * The command should trigger traces, use therefore the high-level Tcl_Obj*
+     * interface.
+     */
+
+    tclVarFlags = (object->nsPtr) ? TCL_LEAVE_ERR_MSG|TCL_NAMESPACE_ONLY : TCL_LEAVE_ERR_MSG;
+    if (likely(valueObj == NULL)) {
+      resultObj = Tcl_ObjGetVar2(interp, nameObj, NULL, tclVarFlags);
+    } else {
+      resultObj = Tcl_ObjSetVar2(interp, nameObj, NULL, valueObj, tclVarFlags);
+    }
   } else {
-    /*fprintf(stderr, "setvar in obj %s: name %s = %s\n", ObjectName(object), ObjStr(nameObj), ObjStr(value));*/
-    resultObj = Tcl_ObjSetVar2(interp, nameObj, NULL, valueObj, flags);
+    /*
+     * The command should not trigger traces, use the low-level TclLookupVar()
+     * interface.
+     */
+    Var *arrayPtr, *varPtr;
+
+    if (likely(valueObj == NULL)) {
+
+      varPtr = TclLookupVar(interp, ObjStr(nameObj), NULL, TCL_LEAVE_ERR_MSG|TCL_PARSE_PART1, "access",
+                            /*createPart1*/ 0, /*createPart2*/ 0, &arrayPtr);
+      if (likely(varPtr != NULL)) {
+        resultObj = varPtr->value.objPtr;
+      } else {
+        resultObj = NULL;
+      }
+
+    } else {
+      Tcl_Obj *oldValuePtr;
+
+      varPtr = TclLookupVar(interp, ObjStr(nameObj), NULL, TCL_LEAVE_ERR_MSG|TCL_PARSE_PART1, "access",
+                            /*createPart1*/ 1, /*createPart2*/ 0, &arrayPtr);
+      oldValuePtr = varPtr->value.objPtr;
+      INCR_REF_COUNT(valueObj);
+      varPtr->value.objPtr = valueObj;
+      if (oldValuePtr != NULL) {
+        DECR_REF_COUNT(oldValuePtr);
+      }
+      resultObj = valueObj;
+    }
   }
   Nsf_PopFrameObj(interp, framePtr);
 
   if (likely(resultObj != NULL)) {
     Tcl_SetObjResult(interp, resultObj);
     return TCL_OK;
   }
+
   return TCL_ERROR;
 }
 
@@ -20216,7 +20255,7 @@
                            &flags, &checkedData, &outObjPtr);
 
     if (likely(result == TCL_OK)) {
-      result = SetInstVar(interp, object, objv[0], outObjPtr);
+      result = SetInstVar(interp, object, objv[0], outObjPtr, NSF_VAR_TRIGGER_TRACE);
     }
 
     if ((flags & NSF_PC_MUST_DECR) != 0u) {
@@ -20225,7 +20264,7 @@
     return result;
 
   } else {
-    return SetInstVar(interp, object, objv[0], objc == 2 ? objv[1] : NULL);
+    return SetInstVar(interp, object, objv[0], objc == 2 ? objv[1] : NULL, NSF_VAR_TRIGGER_TRACE);
   }
 }
 
@@ -27302,16 +27341,17 @@
 
 /*
 cmd var::get NsfVarGetCmd {
-  {-argName "-array" -required 0 -nrargs 0}
+  {-argName "-array" -required 0 -nrargs 0 -type switch}
+  {-argName "-notrace" -required 0 -nrargs 0 -type switch}
   {-argName "object" -required 1 -type object}
   {-argName "varName" -required 1 -type tclobj}
 }
 */
 static int
-NsfVarGetCmd(Tcl_Interp *interp, int withArray,
+NsfVarGetCmd(Tcl_Interp *interp, int withArray, int withNotrace,
              NsfObject *object, Tcl_Obj *varName) {
 
-  return NsfVarSetCmd(interp, withArray, object, varName, NULL);
+  return NsfVarSetCmd(interp, withArray, withNotrace, object, varName, NULL);
 }
 
 /*
@@ -27366,14 +27406,15 @@
 
 /*
 cmd var::set NsfVarSetCmd {
-  {-argName "-array" -required 0 -nrargs 0}
+  {-argName "-array" -required 0 -nrargs 0 -type switch}
+  {-argName "-notrace" -required 0 -nrargs 0 -type switch}
   {-argName "object" -required 1 -type object}
   {-argName "varName" -required 1 -type tclobj}
   {-argName "value" -required 0 -type tclobj}
 }
 */
 static int
-NsfVarSetCmd(Tcl_Interp *interp, int withArray,
+NsfVarSetCmd(Tcl_Interp *interp, int withArray, int withNotrace,
              NsfObject *object, Tcl_Obj *varName, Tcl_Obj *valueObj) {
 
   nonnull_assert(interp != NULL);
@@ -27383,10 +27424,11 @@
   if (unlikely(CheckVarName(interp, ObjStr(varName)) != TCL_OK)) {
     return TCL_ERROR;
   }
+
   if (withArray != 0) {
     return SetInstArray(interp, object, varName, valueObj);
   } else {
-    return SetInstVar(interp, object, varName, valueObj);
+    return SetInstVar(interp, object, varName, valueObj, withNotrace ? 0 : NSF_VAR_TRIGGER_TRACE);
   }
 }
 
@@ -28563,7 +28605,7 @@
   nonnull_assert(interp != NULL);
   nonnull_assert(object != NULL);
 
-  if (object->filterStack || object->mixinStack) {
+  if ((object->filterStack != NULL) || (object->mixinStack != NULL)) {
     CallStackUseActiveFrame(interp, &ctx);
   }
 
@@ -28862,7 +28904,7 @@
     i = 1;
   }
 
-  if (object->filterStack || object->mixinStack) {
+  if ((object->filterStack != NULL) || (object->mixinStack != NULL)) {
     CallStackUseActiveFrame(interp, &ctx);
   }
 
Index: generic/nsfAPI.decls
===================================================================
diff -u -N -r183cd0a9a3d2a37133ac51bb86952e1b522dbf6f -rdadf28efd0707ae40076f49837e6b45ad5b2a989
--- generic/nsfAPI.decls	(.../nsfAPI.decls)	(revision 183cd0a9a3d2a37133ac51bb86952e1b522dbf6f)
+++ generic/nsfAPI.decls	(.../nsfAPI.decls)	(revision dadf28efd0707ae40076f49837e6b45ad5b2a989)
@@ -310,6 +310,7 @@
 } {-nxdoc 1}
 cmd "var::get" NsfVarGetCmd {
   {-argName "-array" -required 0 -nrargs 0 -type switch}
+  {-argName "-notrace" -required 0 -nrargs 0 -type switch}
   {-argName "object" -required 1 -type object}
   {-argName "varName" -required 1 -type tclobj}
 } {-nxdoc 1}
@@ -320,6 +321,7 @@
 } {-nxdoc 1}
 cmd "var::set" NsfVarSetCmd {
   {-argName "-array" -required 0 -nrargs 0 -type switch}
+  {-argName "-notrace" -required 0 -nrargs 0 -type switch}
   {-argName "object" -required 1 -type object}
   {-argName "varName" -required 1 -type tclobj}
   {-argName "value" -required 0 -type tclobj}
Index: generic/nsfAPI.h
===================================================================
diff -u -N -r183cd0a9a3d2a37133ac51bb86952e1b522dbf6f -rdadf28efd0707ae40076f49837e6b45ad5b2a989
--- generic/nsfAPI.h	(.../nsfAPI.h)	(revision 183cd0a9a3d2a37133ac51bb86952e1b522dbf6f)
+++ generic/nsfAPI.h	(.../nsfAPI.h)	(revision dadf28efd0707ae40076f49837e6b45ad5b2a989)
@@ -662,12 +662,12 @@
   NSF_nonnull(1);
 static int NsfVarExistsCmd(Tcl_Interp *interp, int withArray, NsfObject *object, const char *varName)
   NSF_nonnull(1) NSF_nonnull(3) NSF_nonnull(4);
-static int NsfVarGetCmd(Tcl_Interp *interp, int withArray, NsfObject *object, Tcl_Obj *varName)
-  NSF_nonnull(1) NSF_nonnull(3) NSF_nonnull(4);
+static int NsfVarGetCmd(Tcl_Interp *interp, int withArray, int withNotrace, NsfObject *object, Tcl_Obj *varName)
+  NSF_nonnull(1) NSF_nonnull(4) NSF_nonnull(5);
 static int NsfVarImportCmd(Tcl_Interp *interp, NsfObject *object, int nobjc, Tcl_Obj *CONST* nobjv)
   NSF_nonnull(1) NSF_nonnull(2);
-static int NsfVarSetCmd(Tcl_Interp *interp, int withArray, NsfObject *object, Tcl_Obj *varName, Tcl_Obj *value)
-  NSF_nonnull(1) NSF_nonnull(3) NSF_nonnull(4);
+static int NsfVarSetCmd(Tcl_Interp *interp, int withArray, int withNotrace, NsfObject *object, Tcl_Obj *varName, Tcl_Obj *value)
+  NSF_nonnull(1) NSF_nonnull(4) NSF_nonnull(5);
 static int NsfVarUnsetCmd(Tcl_Interp *interp, int withNocomplain, NsfObject *object, Tcl_Obj *varName)
   NSF_nonnull(1) NSF_nonnull(3) NSF_nonnull(4);
 static int NsfOAutonameMethod(Tcl_Interp *interp, NsfObject *obj, int withInstance, int withReset, Tcl_Obj *name)
@@ -2442,11 +2442,12 @@
                      method_definitions[NsfVarGetCmdIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
                      &pc) == TCL_OK)) {
     int withArray = (int )PTR2INT(pc.clientData[0]);
-    NsfObject *object = (NsfObject *)pc.clientData[1];
-    Tcl_Obj *varName = (Tcl_Obj *)pc.clientData[2];
+    int withNotrace = (int )PTR2INT(pc.clientData[1]);
+    NsfObject *object = (NsfObject *)pc.clientData[2];
+    Tcl_Obj *varName = (Tcl_Obj *)pc.clientData[3];
 
     assert(pc.status == 0);
-    return NsfVarGetCmd(interp, withArray, object, varName);
+    return NsfVarGetCmd(interp, withArray, withNotrace, object, varName);
 
   } else {
     
@@ -2484,12 +2485,13 @@
                      method_definitions[NsfVarSetCmdIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
                      &pc) == TCL_OK)) {
     int withArray = (int )PTR2INT(pc.clientData[0]);
-    NsfObject *object = (NsfObject *)pc.clientData[1];
-    Tcl_Obj *varName = (Tcl_Obj *)pc.clientData[2];
-    Tcl_Obj *value = (Tcl_Obj *)pc.clientData[3];
+    int withNotrace = (int )PTR2INT(pc.clientData[1]);
+    NsfObject *object = (NsfObject *)pc.clientData[2];
+    Tcl_Obj *varName = (Tcl_Obj *)pc.clientData[3];
+    Tcl_Obj *value = (Tcl_Obj *)pc.clientData[4];
 
     assert(pc.status == 0);
-    return NsfVarSetCmd(interp, withArray, object, varName, value);
+    return NsfVarSetCmd(interp, withArray, withNotrace, object, varName, value);
 
   } else {
     
@@ -3795,17 +3797,19 @@
   {"object", NSF_ARG_REQUIRED, 1, Nsf_ConvertTo_Object, NULL,NULL,"object",NULL,NULL,NULL,NULL,NULL},
   {"varName", NSF_ARG_REQUIRED, 1, Nsf_ConvertTo_String, NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL}}
 },
-{"::nsf::var::get", NsfVarGetCmdStub, 3, {
+{"::nsf::var::get", NsfVarGetCmdStub, 4, {
   {"-array", 0, 0, Nsf_ConvertTo_Boolean, NULL,NULL,"switch",NULL,NULL,NULL,NULL,NULL},
+  {"-notrace", 0, 0, Nsf_ConvertTo_Boolean, NULL,NULL,"switch",NULL,NULL,NULL,NULL,NULL},
   {"object", NSF_ARG_REQUIRED, 1, Nsf_ConvertTo_Object, NULL,NULL,"object",NULL,NULL,NULL,NULL,NULL},
   {"varName", NSF_ARG_REQUIRED, 1, Nsf_ConvertTo_Tclobj, NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL}}
 },
 {"::nsf::var::import", NsfVarImportCmdStub, 2, {
   {"object", NSF_ARG_REQUIRED, 1, Nsf_ConvertTo_Object, NULL,NULL,"object",NULL,NULL,NULL,NULL,NULL},
   {"args", 0, 1, ConvertToNothing, NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL}}
 },
-{"::nsf::var::set", NsfVarSetCmdStub, 4, {
+{"::nsf::var::set", NsfVarSetCmdStub, 5, {
   {"-array", 0, 0, Nsf_ConvertTo_Boolean, NULL,NULL,"switch",NULL,NULL,NULL,NULL,NULL},
+  {"-notrace", 0, 0, Nsf_ConvertTo_Boolean, NULL,NULL,"switch",NULL,NULL,NULL,NULL,NULL},
   {"object", NSF_ARG_REQUIRED, 1, Nsf_ConvertTo_Object, NULL,NULL,"object",NULL,NULL,NULL,NULL,NULL},
   {"varName", NSF_ARG_REQUIRED, 1, Nsf_ConvertTo_Tclobj, NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL},
   {"value", 0, 1, Nsf_ConvertTo_Tclobj, NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL}}
Index: generic/nsfCmdPtr.c
===================================================================
diff -u -N -r183cd0a9a3d2a37133ac51bb86952e1b522dbf6f -rdadf28efd0707ae40076f49837e6b45ad5b2a989
--- generic/nsfCmdPtr.c	(.../nsfCmdPtr.c)	(revision 183cd0a9a3d2a37133ac51bb86952e1b522dbf6f)
+++ generic/nsfCmdPtr.c	(.../nsfCmdPtr.c)	(revision dadf28efd0707ae40076f49837e6b45ad5b2a989)
@@ -37,8 +37,10 @@
  */
 
 static NSF_INLINE NsfObject* NsfGetObjectFromCmdPtr(Tcl_Command cmd) nonnull(1);
-static NSF_INLINE NsfClass*  NsfGetClassFromCmdPtr(Tcl_Command cmd) nonnull(1);
 static NSF_INLINE ClientData NsfGetClientDataFromCmdPtr(Tcl_Command cmd) nonnull(1);
+#ifdef NSF_C
+static NSF_INLINE NsfClass*  NsfGetClassFromCmdPtr(Tcl_Command cmd) nonnull(1);
+#endif
 
 static NSF_INLINE ClientData
 NsfGetClientDataFromCmdPtr(Tcl_Command cmd) {
@@ -59,6 +61,7 @@
   }
 }
 
+#ifdef NSF_C
 static NSF_INLINE NsfClass*
 NsfGetClassFromCmdPtr(Tcl_Command cmd) {
   ClientData cd;
@@ -73,6 +76,7 @@
     return NULL;
   }
 }
+#endif
 
 static NSF_INLINE NsfObject*
 NsfGetObjectFromCmdPtr(Tcl_Command cmd) {
Index: library/nx/nx.tcl
===================================================================
diff -u -N -rccca1a502b5c9b77ecfd8ce16c59d77b14f0ccfd -rdadf28efd0707ae40076f49837e6b45ad5b2a989
--- library/nx/nx.tcl	(.../nx.tcl)	(revision ccca1a502b5c9b77ecfd8ce16c59d77b14f0ccfd)
+++ library/nx/nx.tcl	(.../nx.tcl)	(revision dadf28efd0707ae40076f49837e6b45ad5b2a989)
@@ -38,7 +38,7 @@
 # SOFTWARE.
 #
 package require nsf
-package provide nx 2.0.0
+package provide nx 2.1.0
 
 namespace eval ::nx {
 
@@ -1117,7 +1117,7 @@
     }
 
     set slotObj [::nx::slotObj -container $container $target $slotname]
-    #puts stderr "[self] *** [list $class create $slotObj] {*}$opts <$initblock>"
+    #puts stderr "SLOTCREATE [self] *** [list $class create $slotObj] {*}$opts <$initblock>"
     set r [$class create $slotObj {*}$opts $initblock]
     #puts stderr "*** returned $r"
     return $r
@@ -1267,6 +1267,7 @@
     {positional}
     {elementtype}
     {multiplicity 1..1}
+    {trace}
   }
 
   # TODO: check, if substdefault/default could work with e.g. alias; otherwise, move substdefault down
@@ -1817,9 +1818,7 @@
     {accessor public}
     {type}
     {settername}
-    valuecmd
-    defaultcmd
-    valuechangedcmd
+    {trace none}
   }
 
   ::nx::VariableSlot public method setCheckedInstVar {-nocomplain:switch object value} {
@@ -1840,8 +1839,13 @@
   }
 
   ::nx::VariableSlot protected method setterRedefinedOptions {} {
-    if {[:info lookup method value=set] ne "::nsf::classes::nx::VariableSlot::value=set"} {
-      # In case the "set" method was provided on the slot, ask nsf to call it directly
+    #
+    # In the :trace = "set" case, the slot will be set via the trace
+    # triggered from the direct assingment. Otherwise, when the
+    # "value=set" method is provided, tell nsf ot call it (e.g. in
+    # configure).
+    #
+    if {${:trace} ne "set" && [:info lookup method value=set] ne "::nsf::classes::nx::VariableSlot::value=set"} {
       return [list slot=[::nsf::self] slotset]
     }
     if {[:info lookup method value=get] ne "::nsf::classes::nx::VariableSlot::value=get"} {
@@ -2063,38 +2067,44 @@
     # creation time of instances, or immediately for per-object slots.
     #
     set __initblock ""
-    set trace {::nsf::directdispatch [::nsf::self] -frame object ::trace}
+    set traceCmd {::nsf::directdispatch [::nsf::self] -frame object ::trace}
 
+    #puts stderr "instance variable trace has value <${:trace}>"
+    if {"default" in ${:trace}} {
+      if {"get" in ${:trace}} {
+        return -code error \
+            "'-trace default' and '-trace get' can't be used together"
+      }
+    }
     # There might be already default values registered on the
-    # class. If so, defaultcmd is ignored.
+    # class. If so, the default trace is ignored.
     if {[info exists :default]} {
-      if {[info exists :defaultcmd]} {
-	  return -code error \
-	      "defaultcmd can't be used together with default value"
+      if {"default" in ${:trace}} {
+        return -code error \
+            "'-trace default' can't be used together with default value"
       }
-      if {[info exists :valuecmd]} {
-	  return -code error \
-	      "valuecmd can't be used together with default value"
+      if {"get" in ${:trace}} {
+        return -code error \
+            "'trace get' can't be used together with default value"
       }
-    } elseif [info exists :defaultcmd] {
-      if {[info exists :valuecmd]} {
-	  return -code error \
-	      "valuecmd can't be used together with defaultcmd"
-      }
+    }
+    if {"default" in ${:trace}} {
+      #puts stderr "DEFAULTCMD [self] trace=${:trace}"
       append __initblock "::nsf::directdispatch [::nsf::self] -frame object :removeTraces \[::nsf::self\] read\n"
-      append __initblock "$trace add variable [list ${:name}] read \
-	\[list [::nsf::self] __default_from_cmd \[::nsf::self\] [list [set :defaultcmd]]\]\n"
-
-    } elseif [info exists :valuecmd] {
+      append __initblock "$traceCmd add variable [list ${:name}] read \
+	\[list [::nsf::self] __trace_default \[::nsf::self\]\]\n"
+    }
+    if {"get" in ${:trace}} {
+      #puts stderr "VALUECMD [self] trace=${:trace}"
       append __initblock "::nsf::directdispatch [::nsf::self] -frame object :removeTraces \[::nsf::self\] read\n"
-      append __initblock "$trace add variable [list ${:name}] read \
-	\[list [::nsf::self] __value_from_cmd \[::nsf::self\] [list [set :valuecmd]]\]\n"
+      append __initblock "$traceCmd add variable [list ${:name}] read \
+	\[list [::nsf::self] __trace_get \[::nsf::self\]\]\n"
     }
-
-    if {[info exists :valuechangedcmd]} {
+    if {"set" in ${:trace}} {
+      #puts stderr "VALUECHANGED [self] trace=${:trace}"
       append __initblock "::nsf::directdispatch [::nsf::self] -frame object :removeTraces \[::nsf::self\] write\n"
-      append __initblock "$trace add variable [list ${:name}] write \
-	\[list [::nsf::self] __value_changed_cmd \[::nsf::self\] [list [set :valuechangedcmd]]\]"
+      append __initblock "$traceCmd add variable [list ${:name}] write \
+	\[list [::nsf::self] __trace_set \[::nsf::self\]\]\n"
     }
 
     if {$__initblock ne ""} {
@@ -2115,14 +2125,30 @@
 	::trace remove variable $var $op [list [::nsf::self] [::nsf::current method] $obj $cmd]
     ::nsf::var::set $obj $var [$obj eval $cmd]
   }
-  ::nx::VariableSlot method __value_from_cmd {obj cmd var sub op} {
-    #puts stderr "GETVAR [::nsf::current method] obj=$obj cmd=$cmd, var=$var, op=$op"
-    ::nsf::var::set $obj [string trimleft $var :] [$obj eval $cmd]
+  # TODO: remove me
+  # ::nx::VariableSlot method __value_from_cmd {obj cmd var sub op} {
+  #   #puts stderr "GETVAR [::nsf::current method] obj=$obj cmd=$cmd, var=$var, op=$op"
+  #   ::nsf::var::set $obj [string trimleft $var :] [$obj eval $cmd]
+  # }
+  #::nx::VariableSlot method __value_changed_cmd {obj method var sub op} {
+  #  #puts "valuechanged obj=$obj cmd=$cmd, var=$var, op=$op"
+  #  eval $cmd
+  #}
+  ::nx::VariableSlot method __trace_default {obj var sub op} {
+    #puts stderr "trace_default call obj=$obj var=$var, sub=<$sub> op=$op"
+    ::nsf::directdispatch $obj -frame object \
+	::trace remove variable $var $op [list [::nsf::self] [::nsf::current method] $obj]
+    ::nsf::var::set $obj $var [:value=default $obj $var]
   }
-  ::nx::VariableSlot method __value_changed_cmd {obj cmd var sub op} {
-    #puts "valuechanged obj=$obj cmd=$cmd, var=$var, op=$op"
-    eval $cmd
+  ::nx::VariableSlot method __trace_get {obj var sub op} {
+    #puts stderr "trace_get call obj=$obj var=$var, sub=<$sub> op=$op"
+    :value=get $obj [string trimleft $var :]
   }
+  ::nx::VariableSlot method __trace_set {obj var sub op} {
+    #puts stderr "trace_set call obj=$obj var=$var, sub=<$sub> op=$op"
+    set var [string trimleft $var :]
+    :value=set $obj $var [::nsf::var::get $obj $var]
+  }
 
   ######################################################################
   # Implementation of (incremental) forwarder operations for
@@ -2167,11 +2193,12 @@
 
   nx::Object method "object variable" {
      {-accessor "none"}
-     {-incremental:switch}
      {-class ""}
      {-configurable:boolean false}
+     {-incremental:switch}
      {-initblock ""}
      {-nocomplain:switch}
+     {-trace}
      spec:parameter
      defaultValue:optional
    } {
@@ -2195,10 +2222,13 @@
       set configurable $opts(-configurable)
     }
 
-    #if {$initblock eq "" && $accessor eq "none" && !$incremental}
-    if {$initblock eq "" && !$configurable && $accessor eq "none" && !$incremental} {
+    if {![info exists trace] && [info exists :trace] && ${:trace} ne "none"} {
+      set trace ${:trace} 
+    }
+    if {$initblock eq "" && !$configurable && !$incremental 
+        && $accessor eq "none" && ![info exists trace]} {
       #
-      # we can build a slot-less variable
+      # Slot-less variable
       #
       #puts "... slotless variable $spec"
 
@@ -2235,13 +2265,15 @@
     #
     # create variable via a slot object
     #
+    set defaultopts [list -accessor $accessor]
+    if {[info exists trace]} {lappend defaultopts -trace $trace}
     set slot [::nx::MetaSlot createFromParameterSpec [self] \
 		  -per-object \
 		  -class $class \
 		  -initblock $initblock \
 		  -incremental=$incremental \
 		  -private=[expr {$accessor eq "private"}] \
-		  -defaultopts [list -accessor $accessor] \
+		  -defaultopts $defaultopts \
 		  $spec \
 		  {*}[expr {[info exists defaultValue] ? [list $defaultValue] : ""}]]
 
@@ -2265,18 +2297,20 @@
 
   Object method "object property" {
     {-accessor ""}
+    {-class ""}
     {-configurable:boolean true}
     {-incremental:switch}
-    {-class ""}
     {-nocomplain:switch}
+    {-trace}
      spec:parameter
     {initblock ""}
   } {
 
-    if {${accessor} eq ""} {
+    if {$accessor eq ""} {
       set accessor [::nsf::dispatch [self] __default_accessor]
       #puts stderr "OBJECT [self] got default accessor ${accessor}"
     }
+    set traceSpec [expr {[info exists trace] ? [list -trace $trace] : ""}]
 
     set r [[self] object variable \
 	       -accessor $accessor \
@@ -2285,25 +2319,36 @@
 	       -initblock $initblock \
 	       -configurable $configurable \
 	       -nocomplain=$nocomplain \
+               {*}$traceSpec \
 	       {*}$spec]
     return $r
   }
 
   nx::Class method variable {
     {-accessor "none"}
-    {-incremental:switch}
     {-class ""}
     {-configurable:boolean false}
+    {-incremental:switch}
     {-initblock ""}
+    {-trace}
     spec:parameter
     defaultValue:optional
   } {
+    set defaultopts [list -accessor $accessor -configurable $configurable]
+    if {[info exists trace]} {
+      foreach t $trace {
+        if {$t ni {none get set default}} {
+          return -code error "invalid value '$t' for trace: '$trace'"
+        }
+      }
+      lappend defaultopts -trace $trace
+    }
     set slot [::nx::MetaSlot createFromParameterSpec [::nsf::self] \
 		  -class $class \
 		  -initblock $initblock \
 		  -incremental=$incremental \
 		  -private=[expr {$accessor eq "private"}] \
-		  -defaultopts [list -accessor $accessor -configurable $configurable] \
+		  -defaultopts $defaultopts \
 		  $spec \
 		  {*}[expr {[info exists defaultValue] ? [list $defaultValue] : ""}]]
     if {[$slot eval {info exists :settername}]} {
@@ -2317,23 +2362,25 @@
 
   nx::Class method property {
     {-accessor ""}
+    {-class ""}
     {-configurable:boolean true}
     {-incremental:switch}
-    {-class ""}
+    {-trace}
     spec:parameter
     {initblock ""}
   } {
-
-    if {${accessor} eq ""} {
+    if {$accessor eq ""} {
       set accessor [::nsf::dispatch [self] __default_accessor]
-      #puts stderr "CLASS [self] got default accessor ${accessor}"
     }
+    set traceSpec [expr {[info exists trace] ? [list -trace $trace] : ""}]
+
     set r [[self] ::nsf::classes::nx::Class::variable \
 	       -accessor $accessor \
 	       -incremental=$incremental \
 	       -class $class \
 	       -configurable $configurable \
 	       -initblock $initblock \
+               {*}$traceSpec \
 	       {*}$spec]
     return $r
   }
Index: library/nx/pkgIndex.tcl
===================================================================
diff -u -N -r96a1e6b90fb931aa05ae49d96f328bf74e552d65 -rdadf28efd0707ae40076f49837e6b45ad5b2a989
--- library/nx/pkgIndex.tcl	(.../pkgIndex.tcl)	(revision 96a1e6b90fb931aa05ae49d96f328bf74e552d65)
+++ library/nx/pkgIndex.tcl	(.../pkgIndex.tcl)	(revision dadf28efd0707ae40076f49837e6b45ad5b2a989)
@@ -1,3 +1,3 @@
-package ifneeded nx 2.0.0 [list source [file join $dir nx.tcl]]
+package ifneeded nx 2.1.0 [list source [file join $dir nx.tcl]]
 package ifneeded nx::class-method 1.0 [list source [file join $dir class-method.tcl]]
 package ifneeded nx::plain-object-method 1.0 [list source [file join $dir plain-object-method.tcl]]
Index: library/xotcl/tests/slottest.xotcl
===================================================================
diff -u -N -r6a55e4e48e5431b7b76916a8dbfb550b4cdc6edb -rdadf28efd0707ae40076f49837e6b45ad5b2a989
--- library/xotcl/tests/slottest.xotcl	(.../slottest.xotcl)	(revision 6a55e4e48e5431b7b76916a8dbfb550b4cdc6edb)
+++ library/xotcl/tests/slottest.xotcl	(.../slottest.xotcl)	(revision dadf28efd0707ae40076f49837e6b45ad5b2a989)
@@ -33,9 +33,18 @@
 proc T2 {var sub op} {c1 set $var t2}
 
 Class C -slots {
-  Attribute create x -defaultcmd {set x 1}
-  Attribute create y -defaultcmd {incr ::hu}
-  Attribute create z -defaultcmd {my trace add variable z read T1}
+  #Attribute create x -defaultcmd {set x 1}
+  #Attribute create y -defaultcmd {incr ::hu}
+  #Attribute create z -defaultcmd {my trace add variable z read T1}
+
+  Attribute create x -trace default
+  x object method value=default {obj property} { return 1 }
+
+  Attribute create y -trace default
+  y object method value=default {obj property} { incr ::hu }
+
+  Attribute create z -trace default
+  z object method value=default {obj property} { $obj trace add variable z read T1 }
 }
 
 C create c1
@@ -60,8 +69,14 @@
 }
 
 Class D -slots {
-  Attribute create x -defaultcmd {set x 2}
-  Attribute create z -defaultcmd {my trace add variable z read T2}
+  #  Attribute create x -defaultcmd {set x 2}
+  #  Attribute create z -defaultcmd {my trace add variable z read T2}
+  Attribute create x -trace default
+  x object method value=default {obj property} { return 2 }
+
+  Attribute create z -trace default
+  z object method value=default {obj property} { $obj trace add variable z read T2 }
+
   ?? self ::D
   ?? {namespace current} ::D::slot
 } -superclass C
@@ -499,7 +514,9 @@
 nx::test case defaultcmd
 set ::hu 0
 Class C -slots {
-  Attribute create x -defaultcmd {incr ::hu; set x 101}
+  # Attribute create x -defaultcmd {incr ::hu; set x 101}
+  Attribute create x -trace default
+  x object method value=default {obj property} { incr ::hu; return 101 }
 }
 C c1
 ? {c1 info vars} "__initcmd"
@@ -583,7 +600,11 @@
 # test case (bug) posted by Neil Hampton
 #
 
-Class Fred -slots { Attribute create a -defaultcmd { set _ 4 } }
+Class Fred -slots {
+  #Attribute create a -defaultcmd { set _ 4 }
+  Attribute create a -trace default
+  a object method value=default {obj property} { return 4 }
+}
 ? {Fred x} ::x
 ? {x a 4} 4
 x move y
@@ -689,118 +710,7 @@
   ? {::nsf::method::property o obar debug} 1
 }
 
-
-
-exit
-
-######################################################################
 #
-# Obsolete content
-#
-######################################################################
-#puts [Person array get __defaults]
-#puts [Person serialize]
-puts [Serializer all]
-eval [Serializer all]
-
-? {p2 salary} 1009
-? {catch {p2 append salary b}} 1
-? {p2 salary} 1009
-#p2 projects add ::o1
-exit
-p1 set x 0
-t {p1 set x} "get instvar value via set"
-t {p1 set x 1} "set instvar value via set"
-
-
-
-Object o1
-proc f {x} {return $x}
-o1 forward myf -earlybinding f
-? {o1 myf abc} abc
-
-rename f ""
-proc f {x} {return 11}
-? {o1 myf abc} 11
-
-Object o2
-o2 proc f {x} {expr {$x*2}}
-o1 forward myf -earlybinding o2 f
-
-? {o1 myf 100} 200
-
-o1 set x 42
-o1 forward x -earlybinding ::nsf::var::set %self %proc
-? [list o1 x] 42
-? [list o1 x 41] 41
-? {o1 x} "get parametercmd via forward (earlybinding)"
-? {o1 x 41} "set parametercmd via forward (earlybinding)"
-
-#obj forward Mixin -default {getter setter} mixin %1  %self
-o1 forward z -default {getter setter} %self
-
-o1 forward myfset -objscope set
-o1 myfset y 102
-? {o1 myfset y} 102
-
-? {o1 myfset y} "get instvar value via forward"
-? {o1 myfset y 122} "set instvar value via forward"
-
-o1 forward myfdset -earlybinding -objscope set
-o1 myfdset y 103
-? {o1 myfdset y} 103
-
-? {o1 myfdset y} "get instvar value via forward -earlybinding"
-? {o1 myfdset y 123} "set instvar value via forward -earlybinding"
-
-::nsf::method::alias o1 myset -frame object ::set
-o1 myset x 101
-? {o1 myset x} 101
-
-? {o1 myset x} "get instvar value via set alias"
-? {o1 myset x 123} "set instvar value via set alias"
-
-
-? {p1 age} "slot read"
-Class P -parameter {age {s -setter sets}}
-P instproc sets {var value} {
-  my set $var $value
-}
-P create p2 -age 345 -s 567
-
-? {p2 age} "parametercmd read"
-? {::nsf::var::set p2 age} "via setinstvar"
-? {p2 s} "parameter read with setter"
-
-
-
-
-Slot create Project::fullbudget \
-    -defaultcmd {$obj set __x 100} \
-    -valuechangedcmd {
-      puts "budget is now [$obj set fullbudget]"
-      $obj set __x [$obj set fullbudget]
-    }
-
-Slot create Project::currentbudget -valuecmd {$obj incr __x -1}
-
-Person p2 -name gustaf
-Person p3 -name frido
-Article a1 -title "My life as a saint" -date "1.1.2006"
-publishes new -written_by p1 -has_published a1
-set p [Project new -name icamp -manager p2 -member add p1 -member add p3]
-$p member add X end
-puts [$p member]
-
-? [list $p fullbudget] 100
-? [list $p fullbudget] 100
-? [list $p currentbudget] 99
-? [list $p currentbudget] 98
-? [list $p fullbudget 200] 200
-? [list $p currentbudget] 199
-
-
-#
 # Local variables:
 #    mode: tcl
 #    tcl-indent-level: 2
Index: tests/accessor.test
===================================================================
diff -u -N -r0a38046eb4aac6c36ac7c72dc8b0fe6da43f7c6e -rdadf28efd0707ae40076f49837e6b45ad5b2a989
--- tests/accessor.test	(.../accessor.test)	(revision 0a38046eb4aac6c36ac7c72dc8b0fe6da43f7c6e)
+++ tests/accessor.test	(.../accessor.test)	(revision dadf28efd0707ae40076f49837e6b45ad5b2a989)
@@ -60,7 +60,7 @@
     ? {c1 cget -p3a} 3
     ? {c1 p3a get} 3
     ? {c1 configure -p3a 3} ""
-    ? {c1 p3a get 3} {invalid argument '3', maybe too many arguments; should be "value=get ?-array? /object/ /varName/"}
+    ? {c1 p3a get 3} {invalid argument '3', maybe too many arguments; should be "value=get ?-array? ?-notrace? /object/ /varName/"}
     ? {c1 p3a set 3} 3
     ? {c1 p3a unset} ""
     ? {c1 cget -p3a} {can't read "p3a": no such variable}
Index: tests/cget.test
===================================================================
diff -u -N -r3946480dcc906b5004bf18ee49b49054fa400e0d -rdadf28efd0707ae40076f49837e6b45ad5b2a989
--- tests/cget.test	(.../cget.test)	(revision 3946480dcc906b5004bf18ee49b49054fa400e0d)
+++ tests/cget.test	(.../cget.test)	(revision dadf28efd0707ae40076f49837e6b45ad5b2a989)
@@ -235,10 +235,9 @@
   # class case with no default
   #
   nx::Class create C
-  C property p {
-    set :valuechangedcmd {
-      #puts stderr "==== C.p valuechangedcmd $obj $var +1"
-      ::nsf::var::set $obj $var [expr {[::nsf::var::set $obj $var] + 1}]
+  C property -trace set p {
+    :public object method value=set {obj var value} {
+      ::nsf::var::set -notrace $obj $var [expr {$value + 1}]
     }
   }
   
@@ -253,10 +252,9 @@
   #
   # class case with default
   #
-  C property {q 100} {
-    set :valuechangedcmd {
-      #puts stderr "C.q valuechangedcmd $obj $var +1"
-      ::nsf::var::set $obj $var [expr [list [::nsf::var::set $obj $var] + 1]]
+  C property -trace set {q 100} {
+    :public object method value=set {obj var value} {
+      ::nsf::var::set -notrace $obj $var [expr {$value + 1}]
     }
   }
   C create c2
@@ -274,10 +272,9 @@
   
   nx::Object create o
   ? {o eval {info exists :A}} 0
-  o object property A {
-    set :valuechangedcmd {
-      #puts stderr "o.A valuechangedcmd $obj $var +1"
-      ::nsf::var::set $obj $var [expr [list [::nsf::var::set $obj $var] + 1]]
+  o object property -trace set A {
+    :public object method value=set {obj var value} {
+      ::nsf::var::set -notrace $obj $var [expr {$value + 1}]
     }
   }
   # puts [o info object variables A]
@@ -294,9 +291,10 @@
   #
   
   ? {o eval {info exists :B}} 0
-  o object property {B 1000} {
-    #puts stderr "o.B valuechangedcmd $obj $var +1"
-    set :valuechangedcmd {::nsf::var::set $obj $var [expr [list [::nsf::var::set $obj $var] + 1]]}
+  o object property -trace set {B 1000} {
+    :public object method value=set {obj var value} {
+      ::nsf::var::set -notrace $obj $var [expr {$value + 1}]
+    }
   }
   
   ? {o eval {info exists :B}} 1
@@ -313,10 +311,9 @@
   # class case with type and no default
   #
   nx::Class create C
-  C property p:integer {
-    set :valuechangedcmd {
-      #puts stderr "C.p valuechangedcmd $obj $var +1"
-      ::nsf::var::set $obj $var [expr [list [::nsf::var::set $obj $var] + 1]]
+  C property -trace set p:integer {
+    :public object method value=set {obj var value} {
+      ::nsf::var::set -notrace $obj $var [expr {$value + 1}]
     }
   }
   
@@ -334,20 +331,18 @@
   # class case with type and default
   #
 
-  ? {C property {q:integer aaa} {
-    set :valuechangedcmd {
-      #puts stderr "C.q valuechangedcmd $obj $var +1"
-      ::nsf::var::set $obj $var [expr [list [::nsf::var::set $obj $var] + 1]]
+  ? {C property -trace set {q:integer aaa} {
+    :public object method value=set {obj var value} {
+      ::nsf::var::set -notrace $obj $var [expr {$value + 1}]
     }
   }} {expected integer but got "aaa" for parameter "q"}
 
   # slot should no exist
   ? {C info slots q} ""
 
-  ? {C property {q:integer 99} {
-    set :valuechangedcmd {
-      #puts stderr "C.q valuechangedcmd $obj $var +1"
-      ::nsf::var::set $obj $var [expr [list [::nsf::var::set $obj $var] + 1]]
+  ? {C property -trace set {q:integer 99} {
+    :public object method value=set {obj var value} {
+      ::nsf::var::set -notrace $obj $var [expr {$value + 1}]
     }
   }} ""
 
@@ -370,10 +365,9 @@
   
   nx::Object create o
   ? {o eval {info exists :A}} 0
-  o object property A:integer {
-    set :valuechangedcmd {
-      #puts stderr "o.A valuechangedcmd $obj $var +1"
-      ::nsf::var::set $obj $var [expr [list [::nsf::var::set $obj $var] + 1]]
+  o object property -trace set A:integer {
+    :public object method value=set {obj var value} {
+      ::nsf::var::set -notrace $obj $var [expr {$value + 1}]
     }
   }
   # puts [o info object variables A]
@@ -392,17 +386,19 @@
   #
   
   ? {o eval {info exists :B}} 0
-  ? {o object property {B:integer x} {
-    #puts stderr "o.B valuechangedcmd $obj $var +1"
-    set :valuechangedcmd {::nsf::var::set $obj $var [expr [list [::nsf::var::set $obj $var] + 1]]}
+  ? {o object property -trace set {B:integer x} {
+    :public object method value=set {obj var value} {
+      ::nsf::var::set -notrace $obj $var [expr {$value + 1}]
+    }
   }} {expected integer but got "x" for parameter "B"}
   ? {o eval {info exists :B}} 0
 
   ? {o info object slots B} ""
 
-  ? {o object property {B:integer 1000} {
-    #puts stderr "o.B valuechangedcmd $obj $var +1"
-    set :valuechangedcmd {::nsf::var::set $obj $var [expr [list [::nsf::var::set $obj $var] + 1]]}
+  ? {o object property -trace set {B:integer 1000} {
+    :public object method value=set {obj var value} {
+      ::nsf::var::set -notrace $obj $var [expr {$value + 1}]
+    }
   }} {}
 
   ? {o info object slots B} {::o::per-object-slot::B}
Index: tests/parameters.test
===================================================================
diff -u -N -r183cd0a9a3d2a37133ac51bb86952e1b522dbf6f -rdadf28efd0707ae40076f49837e6b45ad5b2a989
--- tests/parameters.test	(.../parameters.test)	(revision 183cd0a9a3d2a37133ac51bb86952e1b522dbf6f)
+++ tests/parameters.test	(.../parameters.test)	(revision dadf28efd0707ae40076f49837e6b45ad5b2a989)
@@ -35,7 +35,7 @@
   ? {::nsf::method::alias C foo ::set 1} \
       {invalid argument '1', maybe too many arguments; should be "::nsf::method::alias /object/ ?-per-object? /methodName/ ?-frame method|object|default? ?-protection call-protected|redefine-protected|none? /cmdName/"}
 
-  ? {C eval {:property x -class D}} {invalid argument 'D', maybe too many arguments; should be "::C property ?-accessor /value/? ?-configurable /boolean/? ?-incremental? ?-class /value/? /spec/ ?/initblock/?"} "Test whether the colon prefix is suppressed"
+  ? {C eval {:property x -class D}} {invalid argument 'D', maybe too many arguments; should be "::C property ?-accessor /value/? ?-class /value/? ?-configurable /boolean/? ?-incremental? ?-trace /value/? /spec/ ?/initblock/?"} "Test whether the colon prefix is suppressed"
 }
 
 #######################################################
@@ -1328,14 +1328,21 @@
 
 nx::test case slot-traces {
   ::nx::Object create o {
-    :object property -accessor public a {set :defaultcmd { set _ 4 } }
-    :object property -accessor public b {set :valuecmd { set _ 44 } }
-    :object property -accessor public c {set :valuechangedcmd { ::nsf::var::set $obj $var 999 }}
+    :object property -accessor public -trace default a {
+      :public object method value=default {obj var} {puts stderr V=DEFAULT; return 4 }
+    }
+    :object property -accessor public -trace get b {
+      :public object method value=get {obj var} { return 44 }
+    }
+    :object property -accessor public -trace set c {
+      :public object method value=set {obj var value} { ::nsf::var::set $obj $var 999 }
+    }
   }
 
   ? {o a get} 4
   ? {o b get} 44
   ? {o c set 5} 999
+
   ? {::nsf::object::property o hasperobjectslots} 1
 
   o copy o2
@@ -1346,9 +1353,15 @@
   ? {::nsf::object::property o2 hasperobjectslots} 1
 
   ::nx::Class create C {
-    :property -accessor public a {set :defaultcmd { set _ 4 } }
-    :property -accessor public b {set :valuecmd { set _ 44 } }
-    :property -accessor public c {set :valuechangedcmd { ::nsf::var::set $obj $var 999 }}
+    :property -accessor public -trace default a {
+      :public object method value=default {obj var} { return 4 }
+    }
+    :property -accessor public -trace get b {
+      :public object method value=get {obj property} { return 44 }
+    }
+    :property -accessor public -trace set c {
+      :public object method value=set {obj property value} { ::nsf::var::set $obj $property 999 }
+    }
     :create c1
   }
   ? {c1 a get} 4
@@ -1381,33 +1394,29 @@
   Object create o
 
   ? {o eval {info exists :a}} 0
-  ? {o object property {a 0} {
-    set :defaultcmd {set _ 4}
-  }} "defaultcmd can't be used together with default value"
+  ? {o object property -trace default {a 0} { }} "'-trace default' can't be used together with default value"
 
   ? {o eval {info exists :a}} 0
 
   ? {o eval {info exists :b}} 0
-  ? {o object property {b 0} {
-    set :valuecmd {set _ 44}
-  }} "valuecmd can't be used together with default value"
+  ? {o object property -trace get {b 0} { }} "'trace get' can't be used together with default value"
   ? {o eval {info exists :b}} 0
 
   ? {o eval {info exists :c}} 0
-  ? {o object property c {
-    set :defaultcmd {set _ 4}
-    set :valuecmd {set _ 44}
-  }} "valuecmd can't be used together with defaultcmd"
+  ? {o object property -trace {default get} c { }} "'-trace default' and '-trace get' can't be used together"
   ? {o eval {info exists :c}} 0
 
   #
   # valuechangedcmd + default value are allowed
   #
 
   ? {o eval {info exists :a}} 0
-  o object property -accessor public {a 0} {
-    set :valuechangedcmd {::nsf::var::set $obj $var [expr {[::nsf::var::set $obj $var] + 1}]}
+  o object property -accessor public -trace set {a 0} {
+    :public object method value=set {obj var value} {
+      ::nsf::var::set -notrace $obj $var [expr {$value + 1}]
+    }
   }
+
   ? {o eval {info exists :a}} 1
 
   ? {o a get} 0
@@ -1416,8 +1425,10 @@
   ? {o a set 2} 3
 
   ? {o eval {info exists :A}} 0
-  o object property {A 0} {
-    set :valuechangedcmd {::nsf::var::set $obj $var [expr {[::nsf::var::set $obj $var] + 1}]}
+  o object property -trace set {A 0} {
+    :public object method value=set {obj var value} {
+      ::nsf::var::set -notrace $obj $var [expr {$value + 1}]
+    }
   }
   ? {o eval {info exists :A}} 1
   ? {o cget -A} 0
@@ -1427,21 +1438,16 @@
   # per-class:
   Class create Klass
 
-  ? {Klass property {a 0} {
-    set :defaultcmd {set _ 4}
-  }} "defaultcmd can't be used together with default value"
+  ? {Klass property -trace default {a 0} { }} "'-trace default' can't be used together with default value"
 
-  ? {Klass property {b 0} {
-    set :valuecmd {set _ 44}
-  }} "valuecmd can't be used together with default value"
+  ? {Klass property -trace get {b 0} { }} "'trace get' can't be used together with default value"
 
-  ? {Klass property c {
-    set :defaultcmd {set _ 4}
-    set :valuecmd {set _ 44}
-  }} "valuecmd can't be used together with defaultcmd"
+  ? {Klass property -trace {default get} c { }} "'-trace default' and '-trace get' can't be used together"
 
-  Klass property -accessor public {a 0} {
-    set :valuechangedcmd {::nsf::var::set $obj $var [expr {[::nsf::var::set $obj $var] + 1}]}
+  Klass property -accessor public -trace set {a 0} {
+    :public object method value=set {obj var value} {
+      ::nsf::var::set -notrace $obj $var [expr {$value + 1}]
+    }
   }
 
   Klass create k
@@ -1457,12 +1463,14 @@
   #
   # a) against scalar checkers (as a simplistic case)
 
-  Klass property b:boolean {
-    set :valuechangedcmd {set _ tr1e}
+  Klass property -trace set b:boolean {
+    :public object method value=set {obj property value} {
+      return tr1e
+    }
+
   }
 
   ? {catch {Klass create kk}} 0
-
   #
   # b) Structured trace scripts, containing lists. Check for
   # brace balancedness ...
@@ -1481,18 +1489,15 @@
   # evaluated right away and not fiddled through the parameter handling
   # infrastructure.
   ::nx::Class create CC {
-    :property a:0..n {
-      set :defaultcmd {
-	set _ 4
-      }
+    :property -trace default a:0..n {
+      :public object method value=default {obj property} { return 4 }
     }
-
-    :property b:0..n {set :valuecmd {set _ 44} }
-    :property -accessor public c:0..n {
-      set :valuechangedcmd {
-	::nsf::var::set $obj $var 999
-      }
+    :property -trace get b:0..n {
+      :public object method value=get {obj property} { return 44 }
     }
+    :property -accessor public -trace set c:0..n {
+      :public object method value=set {obj property value} { ::nsf::var::set $obj $property 999 }
+    }
     :create ::cc
   }
 
@@ -2993,6 +2998,157 @@
   ? {$::o1 cget -childof} y
 
 }
+
+nx::test case value=changed {
+
+  nx::Class create C {
+
+    :property a {
+      :public object method value=set {object property value} {
+	incr ::slotset_$property
+        nsf::var::set $object $property [expr {$value + 1}]
+      }
+    }
+
+    :property -trace set b {
+      :public object method value=set {object property value} {
+	incr ::slotset_$property
+        nsf::var::set -notrace $object $property [expr {$value + 1}]
+      }
+    }
+
+    :property -accessor public -trace set c {
+      :public object method value=set {object property value} {
+	incr ::slotset_$property
+        nsf::var::set -notrace $object $property [expr {$value + 1}]
+      }
+    }
+
+    :public method foo {} {
+      set :a 100
+      set :b 100
+      set :c 100
+    }
+  }
+  set ::slotset_a 0
+  set ::slotset_b 0
+  set ::slotset_c 0
+
+  ? {C create c1} ::c1
+  ? {set ::slotset_a} 0
+  ? {set ::slotset_b} 0
+  ? {set ::slotset_c} 0
+
+  c1 configure
+  ? {set ::slotset_a} 0
+  ? {set ::slotset_b} 0
+  ? {set ::slotset_c} 0
+
+  c1 configure -a 1 -b 1 -c 1
+  ? {set ::slotset_a} 1
+  ? {set ::slotset_b} 1
+  ? {set ::slotset_c} 1
+  ? {c1 cget -a} 2
+  ? {c1 cget -b} 2
+  ? {c1 cget -c} 2
+
+  ? {c1 cget -a} 2
+  ? {c1 cget -b} 2
+  ? {c1 cget -c} 2
+
+
+  set ::slotset_a 0
+  set ::slotset_b 0
+  set ::slotset_c 0
+  c1 foo
+  ? {set ::slotset_a} 0
+  ? {set ::slotset_b} 1
+  ? {set ::slotset_c} 1
+  ? {c1 cget -a} 100
+  ? {c1 cget -b} 101
+  ? {c1 cget -c} 101
+
+  set ::slotset_a 0
+  set ::slotset_b 0
+  set ::slotset_c 0
+
+  ? {c1 a set 200} {::c1: unable to dispatch method 'a'}
+  ? {c1 b set 200} {::c1: unable to dispatch method 'b'}
+  ? {c1 c set 200} 201
+  ? {set ::slotset_a} 0
+  ? {set ::slotset_b} 0
+  ? {set ::slotset_c} 1
+}
+
+nx::test case trace-meta-slot {
+
+  ::nx::MetaSlot create ::nsv::TraceVariableSlot -superclass ::nx::VariableSlot {
+    :property {trace {get set}}
+    :public method value=set {obj varName value} {
+      incr ::trace_set
+      #puts stderr "SET nsv_set $obj $varName $value"
+      next
+    }
+    :public method value=get {obj varName} {
+      incr ::trace_get
+      #puts stderr "GET nsv_set $obj $varName"
+      next
+    }
+  }
+
+  set ::trace_set 0
+  set ::trace_get 0
+  nx::Class create Foo {
+
+    :property -class ::nsv::TraceVariableSlot x
+
+    :public method exists {var} { info exists :$var }
+    :public method get {var}    { set :$var }
+    :public method foo {}       { incr :x }
+
+    :create ::f1
+  }
+
+  #
+  # Change the value of ::f1.x via configure
+  #
+  ? {set ::trace_set} 0
+  ? {set ::trace_get} 0
+
+  ? {::f1 configure -x "1"} ""
+
+  ? {set ::trace_set} 2 ;# 2, since the next triggers the default setter, which has no "-notrace"
+  ? {set ::trace_get} 0
+
+  ? {::f1 exists x} 1
+  ? {set ::trace_set} 2
+  ? {set ::trace_get} 1
+
+  ? {::f1 cget -x} "1"
+
+  ? {set ::trace_set} 2
+  ? {set ::trace_get} 3  ;# 3, since the next triggers the default setter, which has no "-notrace"
+
+
+  #
+  # Change the value of ::f1.x via configure again
+  #
+  ? {::f1 configure -x 2} ""
+  ? {::f1 cget -x} "2"
+
+  #
+  # Change the value of ::f1.x via variable changes
+  #
+  set ::trace_set 0
+  set ::trace_get 0
+
+  ? {::f1 foo} "3"
+  ? {set ::trace_set} 1
+  ? {set ::trace_get} 1
+
+  ? {::f1 cget -x} "3"
+}
+
 #
 # Local variables:
 #    mode: tcl