diff --git a/src/proc/control/command-setup.cpp b/src/proc/control/command-setup.cpp
index 284b856d8..8f697221c 100644
--- a/src/proc/control/command-setup.cpp
+++ b/src/proc/control/command-setup.cpp
@@ -39,10 +39,15 @@
 #include "proc/control/command-setup.hpp"
 #include "proc/control/command-instance-manager.hpp"
 
+
 //#include <string>
+#include <tuple>
+#include <utility>
 
 //using std::string;
+using std::tuple;
 using std::function;
+using std::move;
 //using util::cStr;
 //using util::_Fmt;
 
@@ -52,9 +57,14 @@ namespace control {
   namespace error = lumiera::error;
   
   
-  
-  namespace { // implementation helper...
-  }//(End) implementation helper
+  namespace { // implementation details of command setup...
+    
+    using CmdDefEntry = std::tuple<Literal, DefinitionClosure>;
+    
+    std::deque<CmdDefEntry> pendingCmdDefinitions;
+    
+    
+  }//(End) implementation details
   
   
   
@@ -64,22 +74,49 @@ namespace control {
   
   CommandSetup::~CommandSetup() { }
   
+  /** Start a command setup for defining a Proc-Layer command with the given cmdID */
   CommandSetup::CommandSetup(Literal cmdID)
     : cmdID_(cmdID)
     { }
   
   
+  /**
+   * @param definitionBlock anything assignable to `function<void(CommandDef&)>`
+   * @remarks this operation is intended for a very specific usage pattern, as established
+   *          by the macro #COMMAND_DEFINITION. The purpose is to feed a given code block
+   *          into the hidden queue for command definitions, from where it will be issued
+   *          at the lifecycle event ON_BASIC_INIT (typically at start of application `main()`).
+   *          On invocation, the code block is provided with an still unbound CommandDef object,
+   *          which has been registered under the Command-ID as stored in this CommandSetup object.
+   *          The assumption is that this _definition closure_ will care to define the command,
+   *          state capturing and undo operations for the command definition in question. Thus,
+   *          the result of invoking this closure will be to store a complete command prototype
+   *          into the proc::control::CommandRegistry.
+   * @note this operation works by side-effect; the given argument is fed into a hidden static
+   *          queue, but not stored within the object instance.
+   * @warning invoking this assignment _several times on the same CommandSetup object_ will likely
+   *          lead to an invalid state, causing the Lumiera application to fail on start-up. The
+   *          reason for this is the fact that CommandDef rejects duplicate command definitions.
+   *          Moreover, please note that invoking this operation at any point _after_ the
+   *          lifecycle event ON_BASIC_INIT will likely have no effect at all, since the
+   *          given closure will then just sit in the static queue and never be invoked.   
+   */
   CommandSetup&
-  CommandSetup::operator= (function<void(CommandDef&)> definitionBlock)
+  CommandSetup::operator= (DefinitionClosure definitionBlock)
   {
-    UNIMPLEMENTED ("definition queue");
+    if (not definitionBlock)
+      throw error::Invalid ("unbound function/closure provided for CommandSetup"
+                           , error::LUMIERA_ERROR_BOTTOM_VALUE);
+    
+    pendingCmdDefinitions.emplace_front (cmdID_, move(definitionBlock));
+    return *this;
   }
   
   
   size_t
   CommandSetup::pendingCnt()
   {
-    UNIMPLEMENTED ("definition queue");
+    return pendingCmdDefinitions.size();
   }
   
   
diff --git a/src/proc/control/command-setup.hpp b/src/proc/control/command-setup.hpp
index 0ae934afc..00af17f83 100644
--- a/src/proc/control/command-setup.hpp
+++ b/src/proc/control/command-setup.hpp
@@ -74,6 +74,8 @@ namespace control {
   
   class CommandDef;
   
+  using DefinitionClosure = std::function<void(CommandDef&)>;
+  
   
   
   /**
@@ -100,7 +102,7 @@ namespace control {
         }
       
       /** core functionality: provide a command definition block. */
-      CommandSetup& operator= (std::function<void(CommandDef&)>);
+      CommandSetup& operator= (DefinitionClosure);
       
       /** diagnostics / test */
       static size_t pendingCnt();
diff --git a/tests/core/proc/control/command-setup-test.cpp b/tests/core/proc/control/command-setup-test.cpp
index a7538fe68..cca2d07b8 100644
--- a/tests/core/proc/control/command-setup-test.cpp
+++ b/tests/core/proc/control/command-setup-test.cpp
@@ -119,6 +119,8 @@ namespace test {
           CHECK (CommandSetup::pendingCnt() == 0);
           
           def_0 = do_something_pointless;
+          CHECK (CommandSetup::pendingCnt() == 1);
+          
           
           CommandSetup def_1{"test.CommandSetup.def_1"};
           CommandSetup def_2{"test.CommandSetup.def_2"};