Added Visual.ZIndex.

And set ZIndex of adorner layer to top-most.

Perspex.Controls/Primitives/AdornerDecorator.cs

@@ -12,6 +12,7 @@ namespace Perspex.Controls.Primitives
         {
             this.AdornerLayer = new AdornerLayer();
             this.AdornerLayer.Parent = this;
+            this.AdornerLayer.ZIndex = int.MaxValue;
             this.AddVisualChild(this.AdornerLayer);
         }
 

Perspex.SceneGraph/IVisual.cs

@@ -63,6 +63,11 @@ namespace Perspex
         /// </summary>
         IVisual VisualParent { get; }
 
+        /// <summary>
+        /// Gets the Z index of the node.
+        /// </summary>
+        int ZIndex { get; }
+
         /// <summary>
         /// Renders the scene graph node to a <see cref="IDrawingContext"/>.
         /// </summary>

Perspex.SceneGraph/Rendering/RendererBase.cs

@@ -6,6 +6,7 @@
 
 namespace Perspex.Rendering
 {
+    using System.Linq;
     using Perspex.Media;
     using Perspex.Platform;
 
@@ -88,7 +89,7 @@ namespace Perspex.Rendering
                     visual.Render(context);
                     d.Dispose();
 
-                    foreach (var child in visual.VisualChildren)
+                    foreach (var child in visual.VisualChildren.OrderBy(x => x.ZIndex))
                     {
                         this.Render(child, context, translation, transform);
                     }

Perspex.SceneGraph/Visual.cs

@@ -39,6 +39,9 @@ namespace Perspex
         public static readonly PerspexProperty<Origin> TransformOriginProperty =
             PerspexProperty.Register<Visual, Origin>("TransformOrigin", defaultValue: Origin.Default);
 
+        public static readonly PerspexProperty<int> ZIndexProperty =
+            PerspexProperty.Register<Visual, int>("ZIndex");
+
         private PerspexList<IVisual> visualChildren;
 
         private Visual visualParent;
@@ -91,6 +94,12 @@ namespace Perspex
             set { this.SetValue(TransformOriginProperty, value); }
         }
 
+        public int ZIndex
+        {
+            get { return this.GetValue(ZIndexProperty); }
+            set { this.SetValue(ZIndexProperty, value); }
+        }
+
         IPerspexReadOnlyList<IVisual> IVisual.VisualChildren
         {
             get { return this.visualChildren; }
@@ -104,6 +113,7 @@ namespace Perspex
             }
         }
 
+
         public void InvalidateVisual()
         {
             IRenderRoot root = this.GetSelfAndVisualAncestors()