diff --git a/src/gui/model/w-link.hpp b/src/gui/model/w-link.hpp
index b1807fda5..a71e9b6f5 100644
--- a/src/gui/model/w-link.hpp
+++ b/src/gui/model/w-link.hpp
@@ -149,7 +149,7 @@ namespace model {
       explicit
       operator bool()  const
         {
-          return bool(widget_);
+          return bool{widget_};
         }
       
       TAR&
@@ -167,6 +167,10 @@ namespace model {
         }
       
       
+      bool isValid()  const { return bool{*this}; }
+      bool isActive() const { return bool{*this}; }
+      
+      
       /** detach and deactivate this link
        * @note EX_STRONG (but only under the assumption that also
        *       sigc::trackable::remove_destroy_notify_cllback is EX_STRONG)
diff --git a/src/gui/timeline/timeline-gui.cpp b/src/gui/timeline/timeline-gui.cpp
index 8190b4d70..5ea8576d4 100644
--- a/src/gui/timeline/timeline-gui.cpp
+++ b/src/gui/timeline/timeline-gui.cpp
@@ -81,8 +81,12 @@ namespace timeline {
   void
   TimelineGui::buildMutator (lib::diff::TreeMutator::Handle buffer)
   {
-    if (*this)
-      UNIMPLEMENTED ("actually delegate diff application to the target");
+    if (this->isActive())
+      operator*().buildMutator (buffer);  // delegate to TimelineController
+    else                                 //  else when no widget exists...
+      buffer.create(
+        TreeMutator::build()
+          .ignoreAllChanges());       //     ...consume and ignore diff
   }
   
   
diff --git a/src/gui/timeline/timeline-widget.cpp b/src/gui/timeline/timeline-widget.cpp
index cbb72058c..7fcc6db8b 100644
--- a/src/gui/timeline/timeline-widget.cpp
+++ b/src/gui/timeline/timeline-widget.cpp
@@ -73,13 +73,15 @@ namespace timeline {
       UNIMPLEMENTED ("build the timeline UI");
     }
   
+  TimelineWidget::~TimelineWidget() { }
   
-  TimelineWidget::~TimelineWidget()
+  
+  void
+  TimelineWidget::buildMutator (lib::diff::TreeMutator::Handle buff)
   {
+    control_->buildMutator (buff);
   }
   
   
   
-  
-  
 }}// namespace gui::timeline
diff --git a/src/gui/timeline/timeline-widget.hpp b/src/gui/timeline/timeline-widget.hpp
index f8c7a7181..cac87d043 100644
--- a/src/gui/timeline/timeline-widget.hpp
+++ b/src/gui/timeline/timeline-widget.hpp
@@ -113,12 +113,15 @@ namespace timeline {
        */
       TimelineWidget (BusTerm::ID identity, BusTerm::ID trackID, BusTerm& nexus);
       
-     ~TimelineWidget();  
+     ~TimelineWidget();
       
       
       
     public: /* ===== Control interface ===== */
       
+      /** allow for diff mutation (delegated to TimelineController */
+      void buildMutator (lib::diff::TreeMutator::Handle);
+      
     public: /* ===== Signals ===== */
       
     private:/* ===== Events ===== */