diff --git a/src/gui/interact/ui-coord-resolver.hpp b/src/gui/interact/ui-coord-resolver.hpp
index 6340a8a03..f7b901498 100644
--- a/src/gui/interact/ui-coord-resolver.hpp
+++ b/src/gui/interact/ui-coord-resolver.hpp
@@ -59,6 +59,7 @@
 
 #include "lib/error.hpp"
 #include "lib/symbol.hpp"
+#include "lib/format-string.hpp"
 #include "gui/interact/ui-coord.hpp"
 #include "lib/iter-tree-explorer.hpp"
 #include "lib/iter-source.hpp"
@@ -372,7 +373,29 @@ namespace interact {
       UICoordResolver&&
       extend (UICoord const& partialExtensionSpec)
         {
-          UNIMPLEMENTED ("extend by UI-Coordinates");
+          if (not canCover())
+            {
+              uic_ = partialExtensionSpec;
+            }
+          else
+            {
+              ENSURE (res_.isResolved and res_.covfefe);
+              size_t coverable = res_.covfefe->size();
+              auto newContent = partialExtensionSpec.begin();
+              size_t extensionPos = newContent? partialExtensionSpec.indexOf(*newContent) : 0;
+              if (coverable >= extensionPos)
+                throw error::Invalid (util::_Fmt{"Attempt to extend covered path %s with %s "
+                                                 "would overwrite positions %d to %d (incl)"}
+                                                % *res_.covfefe
+                                                % partialExtensionSpec
+                                                % extensionPos
+                                                % coverable);
+              cover();
+              for ( ; newContent; ++newContent, ++extensionPos )
+                overwrite (extensionPos, *newContent);
+            }
+          res_.depth = query_.determineCoverage (this->uic_); // coverage may grow
+          return std::move (*this);
         }
       
       
diff --git a/src/gui/interact/ui-coord.hpp b/src/gui/interact/ui-coord.hpp
index c1be9e7ae..0ad6b43c9 100644
--- a/src/gui/interact/ui-coord.hpp
+++ b/src/gui/interact/ui-coord.hpp
@@ -599,6 +599,14 @@ namespace interact {
           uic_.normalise();
           return std::move (*this);
         }
+      
+      Builder&&
+      overwrite (size_t depth, Literal newSpec)
+        {
+          Literal* storage = uic_.expandPosition (depth);
+          uic_.setContent (storage, newSpec);
+          return std::move (*this);
+        }
     };
   
   
diff --git a/wiki/thinkPad.ichthyo.mm b/wiki/thinkPad.ichthyo.mm
index 3a8c8648e..e64d5a706 100644
--- a/wiki/thinkPad.ichthyo.mm
+++ b/wiki/thinkPad.ichthyo.mm
@@ -8944,6 +8944,13 @@
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1515451127221" ID="ID_130067342" MODIFIED="1515451168209" TEXT="durch (partielle) UI-Coord spec">
 <linktarget COLOR="#4f6f95" DESTINATION="ID_130067342" ENDARROW="Default" ENDINCLINATION="544;89;" ID="Arrow_ID_992203487" SOURCE="ID_1736775031" STARTARROW="None" STARTINCLINATION="704;0;"/>
 <icon BUILTIN="flag-yellow"/>
+<node CREATED="1515455194222" ID="ID_1550640486" MODIFIED="1515455202609" TEXT="brauche (nun doch) overwrite">
+<node CREATED="1515455204572" ID="ID_538708318" MODIFIED="1515455215023" TEXT="im UI-Coord-Builder ansiedeln"/>
+<node CREATED="1515455215779" ID="ID_1744879837" MODIFIED="1515455225131" TEXT="protected....">
+<icon BUILTIN="smiley-neutral"/>
+</node>
+</node>
+<node CREATED="1515455238808" ID="ID_1864948105" MODIFIED="1515455247459" TEXT="Fehlerbehandlung: &#xdc;berlapp finden"/>
 </node>
 </node>
 </node>
@@ -9372,6 +9379,15 @@
 </node>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1515451047192" ID="ID_554336668" MODIFIED="1515451078845" TEXT="erweitern scheitert wegen &#xdc;berlapp">
 <icon BUILTIN="flag-yellow"/>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1515455278659" ID="ID_1749331083" MODIFIED="1515455288490" TEXT="pr&#xe4;ziser Anschlu&#xdf; funktioniert">
+<icon BUILTIN="flag-yellow"/>
+</node>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1515455289417" ID="ID_228177396" MODIFIED="1515455317398" TEXT="&#xdc;berlapp == 1 scheitert">
+<icon BUILTIN="flag-yellow"/>
+</node>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1515455296784" ID="ID_957569216" MODIFIED="1515455313258" TEXT="sinnvolle Fehlermeldung">
+<icon BUILTIN="flag-yellow"/>
+</node>
 </node>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1515449669446" ID="ID_1747646759" MODIFIED="1515449741572" TEXT="partially covered erweitern">
 <icon BUILTIN="flag-yellow"/>