diff --git a/docs/DesignGuidelines.txt b/docs/DesignGuidelines.txt
index a321600313..860957be00 100644
--- a/docs/DesignGuidelines.txt
+++ b/docs/DesignGuidelines.txt
@@ -8,7 +8,10 @@ Coding style:
 - Try to avoid unit circles. This makes it easier to navigate and when unit is
   growing allows to split it.
 - Minimize the number of calls from Interfaces to LCL, when performing an
-  action requested by the LCL.
+  action requested by the LCL. The interfaces only notify the LCL, never forces
+  something. The LCL decides.
+  Naming convention:
+    Notifications for TControl decendants should be named CNxxx.
 - All code must work with all checks (range, io, overflow, stack) on. Beside
   that this helps debugging, some users put these checks into their fpc.cfg, so
   they are applied to whole lazarus. Including packages and examples.
diff --git a/lcl/controls.pp b/lcl/controls.pp
index 7ca7543c55..847ff2edd8 100644
--- a/lcl/controls.pp
+++ b/lcl/controls.pp
@@ -1049,6 +1049,7 @@ type
                                 Lock: boolean); virtual;
     procedure GetPreferredSize(var PreferredWidth, PreferredHeight: integer;
                                Raw: boolean); virtual;
+    procedure CNPreferredSizeChanged;
     procedure InvalidatePreferredSize; virtual;
   public
     constructor Create(TheOwner: TComponent);override;
@@ -2911,6 +2912,9 @@ end.
 { =============================================================================
 
   $Log$
+  Revision 1.300  2005/06/25 14:17:57  mattias
+  added notification method CNPreferredSizeChanged
+
   Revision 1.299  2005/06/22 17:37:06  mattias
   implemented TMouse.SetCursorPos  from Andrew
 
diff --git a/lcl/include/control.inc b/lcl/include/control.inc
index 5a59ce64dd..9561218d1a 100644
--- a/lcl/include/control.inc
+++ b/lcl/include/control.inc
@@ -3460,9 +3460,14 @@ begin
   end;
 end;
 
+procedure TControl.CNPreferredSizeChanged;
+begin
+  InvalidatePreferredSize;
+end;
+
 {------------------------------------------------------------------------------
   procedure TControl.InvalidatePreferredSize;
-  
+
   Invalidate the cache of the preferred size of this and all parent controls.
  ------------------------------------------------------------------------------}
 procedure TControl.InvalidatePreferredSize;
@@ -3536,6 +3541,9 @@ end;
 
 { =============================================================================
   $Log$
+  Revision 1.260  2005/06/25 14:17:57  mattias
+  added notification method CNPreferredSizeChanged
+
   Revision 1.259  2005/06/22 23:04:44  mattias
   implemented default height for gtk TStatusBar and set TStatusBar.AutoSize to true
 
diff --git a/lcl/interfaces/gtk/gtkcallback.inc b/lcl/interfaces/gtk/gtkcallback.inc
index f6f3bb3960..7c4fe6011e 100644
--- a/lcl/interfaces/gtk/gtkcallback.inc
+++ b/lcl/interfaces/gtk/gtkcallback.inc
@@ -232,7 +232,7 @@ begin
       end;
 
       if TheWinControl<>nil then begin
-        TheWinControl.InvalidatePreferredSize;
+        TheWinControl.CNPreferredSizeChanged;
         SetCursor(TheWinControl, crDefault);
         ConnectInternalWidgetsSignals(MainWidget,TheWinControl);
         UpdateWidgetStyleOfControl(TheWinControl);
@@ -2986,6 +2986,9 @@ end;
 { =============================================================================
 
   $Log$
+  Revision 1.280  2005/06/25 14:17:57  mattias
+  added notification method CNPreferredSizeChanged
+
   Revision 1.279  2005/06/03 20:58:23  mattias
   fixed focussing modal forms on gtk intf