changed implementation of PanelSelectionHandler so that custom panelselectionhandlers can inherit that class if they are built in the same project. Also added a Partial Selectionhandler that selects objects that are partially selected if both mousebuttons are pressed.

PartialPanelSelectionHandler is activated by adding a custom extension in your project like this:

[ExtensionFor(typeof(Panel), OverrideExtension = typeof(PanelSelectionHandler))]
public class CustomPartialPanelSelectionHandler : PartialPanelSelectionHandler
{
}

src/AddIns/DisplayBindings/WpfDesign/WpfDesign.Designer/Project/Extensions/PanelSelectionHandler.cs

@@ -52,13 +52,13 @@ namespace ICSharpCode.WpfDesign.Designer.Extensions
 		}
 	}
 	
-	sealed class RangeSelectionGesture : ClickOrDragMouseGesture
+	internal class RangeSelectionGesture : ClickOrDragMouseGesture
 	{
-		DesignItem container;
+		protected DesignItem container;
-		AdornerPanel adornerPanel;
+		protected AdornerPanel adornerPanel;
-		SelectionFrame selectionFrame;
+		protected SelectionFrame selectionFrame;
 		
-		GrayOutDesignerExceptActiveArea grayOut;
+		protected GrayOutDesignerExceptActiveArea grayOut;
 		
 		public RangeSelectionGesture(DesignItem container)
 		{
@@ -100,7 +100,7 @@ namespace ICSharpCode.WpfDesign.Designer.Extensions
 					Math.Abs(startPoint.Y - endPoint.Y)
 				);
 				
-				ICollection<DesignItem> items = GetChildDesignItemsInContainer(container, new RectangleGeometry(frameRect));
+				ICollection<DesignItem> items = GetChildDesignItemsInContainer(new RectangleGeometry(frameRect));
 				if (items.Count == 0) {
 					items.Add(container);
 				}
@@ -109,8 +109,7 @@ namespace ICSharpCode.WpfDesign.Designer.Extensions
 			Stop();
 		}
 		
-		static ICollection<DesignItem> GetChildDesignItemsInContainer(
+		protected virtual ICollection<DesignItem> GetChildDesignItemsInContainer(Geometry geometry)
-			DesignItem container, Geometry geometry)
 		{
 			HashSet<DesignItem> resultItems = new HashSet<DesignItem>();
 			ViewService viewService = container.Services.View;

src/AddIns/DisplayBindings/WpfDesign/WpfDesign.Designer/Project/Extensions/PartialPanelSelectionHandler.cs

@@ -0,0 +1,108 @@
+/*
+ * Created by SharpDevelop.
+ * User: trubra
+ * Date: 2014-08-06
+ * Time: 14:13
+ * 
+ * To change this template use Tools | Options | Coding | Edit Standard Headers.
+ */
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Input;
+using System.Windows.Media;
+
+using ICSharpCode.WpfDesign.Adorners;
+using ICSharpCode.WpfDesign.Designer.Controls;
+using ICSharpCode.WpfDesign.Designer.Services;
+using ICSharpCode.WpfDesign.Extensions;
+
+namespace ICSharpCode.WpfDesign.Designer.Extensions
+{
+	public class PartialPanelSelectionHandler : BehaviorExtension, IHandlePointerToolMouseDown
+    {
+        protected override void OnInitialized()
+        {
+            base.OnInitialized();
+            this.ExtendedItem.AddBehavior(typeof(IHandlePointerToolMouseDown), this);
+        }
+
+        public new void HandleSelectionMouseDown(IDesignPanel designPanel, MouseButtonEventArgs e, DesignPanelHitTestResult result)
+        {
+            if (e.ChangedButton == MouseButton.Left && MouseGestureBase.IsOnlyButtonPressed(e, MouseButton.Left))
+            {
+                e.Handled = true;
+                new PartialRangeSelectionGesture(result.ModelHit).Start(designPanel, e);
+            }
+        }
+    }
+
+    /// <summary>
+    /// 
+    /// </summary>
+    internal class PartialRangeSelectionGesture : RangeSelectionGesture
+    {
+        public PartialRangeSelectionGesture(DesignItem container)
+            : base(container)
+        {
+        }
+
+        protected override ICollection<DesignItem> GetChildDesignItemsInContainer(Geometry geometry)
+        {
+            HashSet<DesignItem> resultItems = new HashSet<DesignItem>();
+            ViewService viewService = container.Services.View;
+
+            HitTestFilterCallback filterCallback = delegate(DependencyObject potentialHitTestTarget)
+            {
+                FrameworkElement element = potentialHitTestTarget as FrameworkElement;
+                if (element != null)
+                {
+                    // ensure we are able to select elements with width/height=0
+                    if (element.ActualWidth == 0 || element.ActualHeight == 0)
+                    {
+                        DependencyObject tmp = element;
+                        DesignItem model = null;
+                        while (tmp != null)
+                        {
+                            model = viewService.GetModel(tmp);
+                            if (model != null) break;
+                            tmp = VisualTreeHelper.GetParent(tmp);
+                        }
+                        if (model != container)
+                        {
+                            resultItems.Add(model);
+                            return HitTestFilterBehavior.ContinueSkipChildren;
+                        }
+                    }
+                }
+                return HitTestFilterBehavior.Continue;
+            };
+
+            HitTestResultCallback resultCallback = delegate(HitTestResult result)
+            {
+                if (((GeometryHitTestResult)result).IntersectionDetail == IntersectionDetail.FullyInside || (Mouse.RightButton== MouseButtonState.Pressed && ((GeometryHitTestResult)result).IntersectionDetail == IntersectionDetail.Intersects))
+                {
+                    // find the model for the visual contained in the selection area
+                    DependencyObject tmp = result.VisualHit;
+                    DesignItem model = null;
+                    while (tmp != null)
+                    {
+                        model = viewService.GetModel(tmp);
+                        if (model != null) break;
+                        tmp = VisualTreeHelper.GetParent(tmp);
+                    }
+                    if (model != container)
+                    {
+                        resultItems.Add(model);
+                    }
+                }
+                return HitTestResultBehavior.Continue;
+            };
+
+            VisualTreeHelper.HitTest(container.View, filterCallback, resultCallback, new GeometryHitTestParameters(geometry));
+            return resultItems;
+        }
+    }
+}

src/AddIns/DisplayBindings/WpfDesign/WpfDesign.Designer/Project/WpfDesign.Designer.csproj

@@ -84,6 +84,7 @@
       <Link>Configuration\GlobalAssemblyInfo.cs</Link>
     </Compile>
     <Compile Include="Controls\RenderTransformOriginThumb.cs" />
+    <Compile Include="Extensions\PartialPanelSelectionHandler.cs" />
     <Compile Include="Extensions\RightClickContextMenu.xaml.cs">
       <DependentUpon>RightClickContextMenu.xaml</DependentUpon>
       <SubType>Code</SubType>