diff --git a/src/lib/diff/tree-diff-mutator-binding.cpp b/src/lib/diff/tree-diff-mutator-binding.cpp
index bc6e5a7c1..305476f17 100644
--- a/src/lib/diff/tree-diff-mutator-binding.cpp
+++ b/src/lib/diff/tree-diff-mutator-binding.cpp
@@ -259,8 +259,8 @@ namespace diff{
   void
   TreeDiffMutatorBinding::__failMismatch (GenNode const& spec, Literal oper)
   {
-    throw error::State(_Fmt("Unable to %s element %s. Current target binding "
-                            "did not match as expected") % oper % spec
+    throw error::State(_Fmt("Unable to %s element %s. Current shape of target "
+                            "data does not match expectations") % oper % spec
                       , LUMIERA_ERROR_DIFF_CONFLICT);
   }
   
@@ -273,36 +273,13 @@ namespace diff{
   void
   TreeDiffMutatorBinding::__expect_valid_parent_scope (GenNode::ID const& idi)
   {
-    
+    if (0 == scopeManger_->depth())
+      throw error::Fatal(_Fmt("Diff application floundered after leaving scope %s; "
+                              "unbalanced nested scopes, diff attempts to pop root.") % idi.getSym()
+                        , LUMIERA_ERROR_DIFF_CONFLICT);
   }
   
   
-  /* == Forwarding: mutation primitives == */
-  
-  bool
-  TreeDiffMutatorBinding::matchSrc (GenNode const& n)
-  {
-    UNIMPLEMENTED("ensure the next source element matches with given spec");
-  }
-  
-  void
-  TreeDiffMutatorBinding::assignElm (GenNode const& n)
-  {
-    UNIMPLEMENTED("locate already accepted element and assign given new payload");
-  }
-  
-  void
-  TreeDiffMutatorBinding::open_subScope (GenNode const& n)
-  {
-    UNIMPLEMENTED("locate already accepted element and open recursive sub-scope for mutation");
-  }
-  
-  void
-  TreeDiffMutatorBinding::close_subScope()
-  {
-    UNIMPLEMENTED("finish and leave sub scope and return to invoking parent scope");
-  }
-  
   
   
   /* == Implementation of the list diff application primitives == */
@@ -364,7 +341,8 @@ namespace diff{
   void
   TreeDiffMutatorBinding::set (GenNode const& n)
   {
-    assignElm (n);
+    if (not treeMutator_->assignElm(n))
+      __failMismatch (n, "assign");
   }
   
   /** open nested scope to apply diff to child object */
diff --git a/src/lib/diff/tree-mutator-collection-binding.hpp b/src/lib/diff/tree-mutator-collection-binding.hpp
index 079f92188..d1d207073 100644
--- a/src/lib/diff/tree-mutator-collection-binding.hpp
+++ b/src/lib/diff/tree-mutator-collection-binding.hpp
@@ -327,8 +327,7 @@
             if (binding_.isApplicable(spec))
               {
                 Iter target_found = binding_.locate (spec);
-                return target_found? binding_.assign (*target_found, spec)
-                                   : false;
+                return target_found and binding_.assign (*target_found, spec);
               }
             else
               return PAR::assignElm (spec);
@@ -342,8 +341,7 @@
             if (binding_.isApplicable(spec))
               {
                 Iter target_found = binding_.locate (spec);
-                return target_found? binding_.openSub (*target_found, spec.idi, targetBuff)
-                                   : false;
+                return target_found and binding_.openSub (*target_found, spec.idi, targetBuff);
               }
             else
               return PAR::mutateChild (spec, targetBuff);
diff --git a/wiki/thinkPad.ichthyo.mm b/wiki/thinkPad.ichthyo.mm
index 931891972..174cbe735 100644
--- a/wiki/thinkPad.ichthyo.mm
+++ b/wiki/thinkPad.ichthyo.mm
@@ -4243,7 +4243,7 @@
 <icon BUILTIN="full-4"/>
 <node CREATED="1464305377785" ID="ID_396910166" MODIFIED="1464306126692" TEXT="Vor&#xfc;berlegungen">
 <icon BUILTIN="pencil"/>
-<node CREATED="1464305417066" FOLDED="true" ID="ID_1059660516" MODIFIED="1464306127933" TEXT="w&#xfc;nschenswert">
+<node CREATED="1464305417066" FOLDED="true" ID="ID_1059660516" MODIFIED="1472141092653" TEXT="w&#xfc;nschenswert">
 <icon BUILTIN="help"/>
 <node CREATED="1464305708891" ID="ID_1184917831" MODIFIED="1464305711647" TEXT="Vorteile">
 <node CREATED="1464305431944" ID="ID_426248387" MODIFIED="1464305641440" TEXT="den RecordContentMutator loswerden"/>
@@ -4514,7 +4514,7 @@
 </node>
 <node CREATED="1469544027620" HGAP="38" ID="ID_1475348824" MODIFIED="1469544049582" TEXT="Storage-Probleme" VSHIFT="11">
 <icon BUILTIN="messagebox_warning"/>
-<node CREATED="1469544055624" ID="ID_390940604" MODIFIED="1469544066153" TEXT="Beobachtung: Template-bloat">
+<node CREATED="1469544055624" FOLDED="true" ID="ID_390940604" MODIFIED="1472140990090" TEXT="Beobachtung: Template-bloat">
 <icon BUILTIN="stop-sign"/>
 <node CREATED="1469544072709" ID="ID_16055877" MODIFIED="1469544083016" TEXT="Ursache: wir generieren die Klasse jedesmal neu"/>
 <node CREATED="1469544084220" ID="ID_1247343007" MODIFIED="1469544104909" TEXT="...obwohl keinerlei Bezug zum Target-Typ vorliegt">
@@ -4537,7 +4537,7 @@
 <arrowlink COLOR="#503382" DESTINATION="ID_48737788" ENDARROW="Default" ENDINCLINATION="8;131;" ID="Arrow_ID_579805576" STARTARROW="None" STARTINCLINATION="535;0;"/>
 </node>
 </node>
-<node CREATED="1469544264955" HGAP="35" ID="ID_366424331" MODIFIED="1469544292540" VSHIFT="16">
+<node CREATED="1469544264955" FOLDED="true" HGAP="35" ID="ID_366424331" MODIFIED="1472140986107" VSHIFT="16">
 <richcontent TYPE="NODE"><html>
   <head>
     
@@ -4656,7 +4656,7 @@
 </node>
 </node>
 </node>
-<node CREATED="1469545080826" HGAP="41" ID="ID_268789302" MODIFIED="1469738253120" VSHIFT="17">
+<node CREATED="1469545080826" FOLDED="true" HGAP="41" ID="ID_268789302" MODIFIED="1472140983547" VSHIFT="17">
 <richcontent TYPE="NODE"><html>
   <head>
     
@@ -4828,6 +4828,7 @@
 <node CREATED="1472121965308" ID="ID_292673963" MODIFIED="1472121974646" TEXT="Verb delegiert an Mutator-Primitive"/>
 <node CREATED="1472121976018" ID="ID_421028989" MODIFIED="1472121995995" TEXT="Fehlerbehandlung anhand R&#xfc;ckgabewert dieser"/>
 <node CREATED="1472122015157" ID="ID_151735071" MODIFIED="1472122038334" TEXT="sinnvolle interne Fehler-Funktionen aufbauen"/>
+<node CREATED="1472141026525" ID="ID_671819323" MODIFIED="1472141034511" TEXT="Scope-Wechsel"/>
 </node>
 <node CREATED="1465860740971" ID="ID_1662787747" MODIFIED="1465860752949" TEXT="Unit-Test">
 <icon BUILTIN="pencil"/>