diff --git a/samples/ControlCatalog/Pages/CalendarDatePickerPage.xaml b/samples/ControlCatalog/Pages/CalendarDatePickerPage.xaml
index 3e50bf8a08..2fe16ba8e3 100644
--- a/samples/ControlCatalog/Pages/CalendarDatePickerPage.xaml
+++ b/samples/ControlCatalog/Pages/CalendarDatePickerPage.xaml
@@ -1,5 +1,7 @@
 <UserControl xmlns="https://github.com/avaloniaui"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="clr-namespace:ControlCatalog.ViewModels"
+             x:DataType="vm:MainWindowViewModel"
              x:Class="ControlCatalog.Pages.CalendarDatePickerPage">
   <StackPanel Orientation="Vertical" Spacing="4">
     <TextBlock Classes="h2">A control for selecting dates with a calendar drop-down</TextBlock>
@@ -39,6 +41,9 @@
                 
         <TextBlock Text="Disabled"/>
         <CalendarDatePicker IsEnabled="False"/>
+        
+        <TextBlock Text="Validation Example"/>
+        <CalendarDatePicker SelectedDate="{CompiledBinding ValidatedDateExample, Mode=TwoWay}"/>
       </StackPanel>
 
     </StackPanel> 
diff --git a/samples/ControlCatalog/ViewModels/MainWindowViewModel.cs b/samples/ControlCatalog/ViewModels/MainWindowViewModel.cs
index 4b3cfa9c9d..2b0c30f311 100644
--- a/samples/ControlCatalog/ViewModels/MainWindowViewModel.cs
+++ b/samples/ControlCatalog/ViewModels/MainWindowViewModel.cs
@@ -5,6 +5,7 @@ using Avalonia.Controls.Notifications;
 using Avalonia.Dialogs;
 using Avalonia.Platform;
 using System;
+using System.ComponentModel.DataAnnotations;
 using MiniMvvm;
 
 namespace ControlCatalog.ViewModels
@@ -164,5 +165,17 @@ namespace ControlCatalog.ViewModels
         public MiniCommand ExitCommand { get; }
 
         public MiniCommand ToggleMenuItemCheckedCommand { get; }
+
+        private DateTime? _validatedDateExample;
+
+        /// <summary>
+        ///    A required DateTime which should demonstrate validation for the DateTimePicker
+        /// </summary>
+        [Required]
+        public DateTime? ValidatedDateExample
+        {
+            get => _validatedDateExample;
+            set => this.RaiseAndSetIfChanged(ref _validatedDateExample, value);
+        }
     }
 }
diff --git a/src/Avalonia.Controls/Calendar/CalendarDatePicker.cs b/src/Avalonia.Controls/Calendar/CalendarDatePicker.cs
index a856ee071c..cd9c80d3e0 100644
--- a/src/Avalonia.Controls/Calendar/CalendarDatePicker.cs
+++ b/src/Avalonia.Controls/Calendar/CalendarDatePicker.cs
@@ -185,7 +185,8 @@ namespace Avalonia.Controls
             AvaloniaProperty.RegisterDirect<CalendarDatePicker, DateTime?>(
                 nameof(SelectedDate),
                 o => o.SelectedDate,
-                (o, v) => o.SelectedDate = v);
+                (o, v) => o.SelectedDate = v,
+                enableDataValidation: true);
 
         public static readonly StyledProperty<CalendarDatePickerFormat> SelectedDateFormatProperty =
             AvaloniaProperty.Register<CalendarDatePicker, CalendarDatePickerFormat>(
@@ -533,13 +534,11 @@ namespace Avalonia.Controls
             }
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void UpdateDataValidation<T>(AvaloniaProperty<T> property, BindingValue<T> value)
         {
-            base.OnPropertyChanged(change);
-
-            if (change.Property == SelectedDateProperty)
+            if (property == SelectedDateProperty)
             {
-                DataValidationErrors.SetError(this, change.NewValue.Error);
+                DataValidationErrors.SetError(this, value.Error);
             }
         }
 
diff --git a/src/Avalonia.Themes.Fluent/Controls/CalendarDatePicker.xaml b/src/Avalonia.Themes.Fluent/Controls/CalendarDatePicker.xaml
index 6c4e94caf1..26c3bbc19f 100644
--- a/src/Avalonia.Themes.Fluent/Controls/CalendarDatePicker.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/CalendarDatePicker.xaml
@@ -33,6 +33,7 @@
     
     <Setter Property="Template">
       <ControlTemplate>
+        <DataValidationErrors>
         <Grid ColumnDefinitions="*,Auto">
 
           <Grid.Styles>
@@ -107,7 +108,6 @@
                    Padding="{TemplateBinding Padding}"
                    Watermark="{TemplateBinding Watermark}"
                    UseFloatingWatermark="{TemplateBinding UseFloatingWatermark}"
-                   DataValidationErrors.Errors="{TemplateBinding (DataValidationErrors.Errors)}"
                    VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
                    HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
                    Grid.Column="0"/>
@@ -136,8 +136,12 @@
                       DisplayDateEnd="{TemplateBinding DisplayDateEnd}" />
           </Popup>
         </Grid>
+        </DataValidationErrors>
       </ControlTemplate>
     </Setter>
   </Style>
   
+  <Style Selector="CalendarDatePicker:error TextBox /template/ Border#PART_BorderElement">
+    <Setter Property="BorderBrush" Value="{DynamicResource SystemControlErrorTextForegroundBrush}"/>
+  </Style>
 </Styles>
diff --git a/src/Avalonia.Themes.Fluent/Controls/ListBox.xaml b/src/Avalonia.Themes.Fluent/Controls/ListBox.xaml
index 47704c12bd..1b4d66405b 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ListBox.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ListBox.xaml
@@ -20,6 +20,7 @@
     <Setter Property="Template">
       <ControlTemplate>
         <Border Name="border"
+                ClipToBounds="{TemplateBinding ClipToBounds}"
                 Background="{TemplateBinding Background}"
                 BorderBrush="{TemplateBinding BorderBrush}"
                 BorderThickness="{TemplateBinding BorderThickness}"
diff --git a/src/Avalonia.Visuals/ApiCompatBaseline.txt b/src/Avalonia.Visuals/ApiCompatBaseline.txt
index dcb3246a63..68e3673cfe 100644
--- a/src/Avalonia.Visuals/ApiCompatBaseline.txt
+++ b/src/Avalonia.Visuals/ApiCompatBaseline.txt
@@ -7,6 +7,9 @@ InterfacesShouldHaveSameMembers : Interface member 'public System.Threading.Task
 MembersMustExist : Member 'public System.Threading.Tasks.Task Avalonia.Animation.PageSlide.Start(Avalonia.Visual, Avalonia.Visual, System.Boolean)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public void Avalonia.Media.GlyphRun..ctor()' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public void Avalonia.Media.GlyphRun.GlyphTypeface.set(Avalonia.Media.GlyphTypeface)' does not exist in the implementation but it does exist in the contract.
+CannotSealType : Type 'Avalonia.Media.Pen' is actually (has the sealed modifier) sealed in the implementation but not sealed in the contract.
+MembersMustExist : Member 'protected void Avalonia.Media.Pen.AffectsRender<T>(Avalonia.AvaloniaProperty[])' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'protected void Avalonia.Media.Pen.RaiseInvalidated(System.EventArgs)' does not exist in the implementation but it does exist in the contract.
 TypeCannotChangeClassification : Type 'Avalonia.Media.Immutable.ImmutableSolidColorBrush' is a 'class' in the implementation but is a 'struct' in the contract.
 MembersMustExist : Member 'public void Avalonia.Media.TextFormatting.DrawableTextRun.Draw(Avalonia.Media.DrawingContext)' does not exist in the implementation but it does exist in the contract.
 CannotAddAbstractMembers : Member 'public void Avalonia.Media.TextFormatting.DrawableTextRun.Draw(Avalonia.Media.DrawingContext, Avalonia.Point)' is abstract in the implementation but is missing in the contract.
@@ -83,4 +86,4 @@ InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Size Avaloni
 InterfacesShouldHaveSameMembers : Interface member 'public System.TimeSpan Avalonia.Platform.IPlatformSettings.TouchDoubleClickTime' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Size Avalonia.Platform.IPlatformSettings.TouchDoubleClickSize.get()' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public System.TimeSpan Avalonia.Platform.IPlatformSettings.TouchDoubleClickTime.get()' is present in the implementation but not in the contract.
-Total Issues: 84
+Total Issues: 87
diff --git a/src/Avalonia.Visuals/Media/Pen.cs b/src/Avalonia.Visuals/Media/Pen.cs
index 7c966a35cf..65ba851100 100644
--- a/src/Avalonia.Visuals/Media/Pen.cs
+++ b/src/Avalonia.Visuals/Media/Pen.cs
@@ -7,7 +7,7 @@ namespace Avalonia.Media
     /// <summary>
     /// Describes how a stroke is drawn.
     /// </summary>
-    public class Pen : AvaloniaObject, IPen
+    public sealed class Pen : AvaloniaObject, IPen, IWeakEventSubscriber<EventArgs>
     {
         /// <summary>
         /// Defines the <see cref="Brush"/> property.
@@ -45,6 +45,10 @@ namespace Avalonia.Media
         public static readonly StyledProperty<double> MiterLimitProperty =
             AvaloniaProperty.Register<Pen, double>(nameof(MiterLimit), 10.0);
 
+        private EventHandler? _invalidated;
+        private IAffectsRender? _subscribedToBrush;
+        private IAffectsRender? _subscribedToDashes;
+        
         /// <summary>
         /// Initializes a new instance of the <see cref="Pen"/> class.
         /// </summary>
@@ -96,17 +100,6 @@ namespace Avalonia.Media
             DashStyle = dashStyle;
         }
 
-        static Pen()
-        {
-            AffectsRender<Pen>(
-                BrushProperty,
-                ThicknessProperty,
-                DashStyleProperty,
-                LineCapProperty,
-                LineJoinProperty,
-                MiterLimitProperty);
-        }
-
         /// <summary>
         /// Gets or sets the brush used to draw the stroke.
         /// </summary>
@@ -116,6 +109,11 @@ namespace Avalonia.Media
             set => SetValue(BrushProperty, value);
         }
 
+        private static readonly WeakEvent<IAffectsRender, EventArgs> InvalidatedWeakEvent =
+            WeakEvent.Register<IAffectsRender>(
+                (s, h) => s.Invalidated += h,
+                (s, h) => s.Invalidated -= h);
+
         /// <summary>
         /// Gets or sets the stroke thickness.
         /// </summary>
@@ -165,7 +163,19 @@ namespace Avalonia.Media
         /// <summary>
         /// Raised when the pen changes.
         /// </summary>
-        public event EventHandler? Invalidated;
+        public event EventHandler? Invalidated
+        {
+            add
+            {
+                _invalidated += value;
+                UpdateSubscriptions();
+            }
+            remove
+            {
+                _invalidated -= value; 
+                UpdateSubscriptions();
+            }
+        }
 
         /// <summary>
         /// Creates an immutable clone of the brush.
@@ -182,68 +192,42 @@ namespace Avalonia.Media
                 MiterLimit);
         }
 
-        /// <summary>
-        /// Marks a property as affecting the pen's visual representation.
-        /// </summary>
-        /// <param name="properties">The properties.</param>
-        /// <remarks>
-        /// After a call to this method in a pen's static constructor, any change to the
-        /// property will cause the <see cref="Invalidated"/> event to be raised on the pen.
-        /// </remarks>
-        protected static void AffectsRender<T>(params AvaloniaProperty[] properties)
-            where T : Pen
+        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
         {
-            static void Invalidate(AvaloniaPropertyChangedEventArgs e)
-            {
-                if (e.Sender is T sender)
-                {
-                    sender.RaiseInvalidated(EventArgs.Empty);
-                }
-            }
+            _invalidated?.Invoke(this, EventArgs.Empty);
+            if(change.Property == BrushProperty)
+                UpdateSubscription(ref _subscribedToBrush, Brush);
+            if(change.Property == DashStyleProperty)
+                UpdateSubscription(ref _subscribedToDashes, DashStyle);
+            base.OnPropertyChanged(change);
+        }
 
-            static void InvalidateAndSubscribe(AvaloniaPropertyChangedEventArgs e)
+        
+        void UpdateSubscription(ref IAffectsRender? field, object? value)
+        {
+            if ((_invalidated == null || field != value) && field != null)
             {
-                if (e.Sender is T sender)
-                {
-                    if (e.OldValue is IAffectsRender oldValue)
-                    {
-                        WeakEventHandlerManager.Unsubscribe<EventArgs, T>(
-                            oldValue,
-                            nameof(oldValue.Invalidated),
-                            sender.AffectsRenderInvalidated);
-                    }
-
-                    if (e.NewValue is IAffectsRender newValue)
-                    {
-                        WeakEventHandlerManager.Subscribe<IAffectsRender, EventArgs, T>(
-                            newValue,
-                            nameof(newValue.Invalidated),
-                            sender.AffectsRenderInvalidated);
-                    }
-
-                    sender.RaiseInvalidated(EventArgs.Empty);
-                }
+                InvalidatedWeakEvent.Unsubscribe(field, this);
+                field = null;
             }
 
-            foreach (var property in properties)
+            if (_invalidated != null && field != value && value is IAffectsRender affectsRender)
             {
-                if (property.CanValueAffectRender())
-                {
-                    property.Changed.Subscribe(e => InvalidateAndSubscribe(e));
-                }
-                else
-                {
-                    property.Changed.Subscribe(e => Invalidate(e));
-                }
+                InvalidatedWeakEvent.Subscribe(affectsRender, this);
+                field = affectsRender;
             }
         }
 
-        /// <summary>
-        /// Raises the <see cref="Invalidated"/> event.
-        /// </summary>
-        /// <param name="e">The event args.</param>
-        protected void RaiseInvalidated(EventArgs e) => Invalidated?.Invoke(this, e);
-
-        private void AffectsRenderInvalidated(object? sender, EventArgs e) => RaiseInvalidated(EventArgs.Empty);
+        void UpdateSubscriptions()
+        {
+            UpdateSubscription(ref _subscribedToBrush, Brush);
+            UpdateSubscription(ref _subscribedToDashes, DashStyle);
+        }
+        
+        void IWeakEventSubscriber<EventArgs>.OnEvent(object? sender, WeakEvent ev, EventArgs e)
+        {
+            if (ev == InvalidatedWeakEvent) 
+                _invalidated?.Invoke(this, EventArgs.Empty);
+        }
     }
 }