diff --git a/samples/ControlCatalog/Pages/DataGridPage.xaml b/samples/ControlCatalog/Pages/DataGridPage.xaml
index 6817d0698e..323eaa3463 100644
--- a/samples/ControlCatalog/Pages/DataGridPage.xaml
+++ b/samples/ControlCatalog/Pages/DataGridPage.xaml
@@ -1,5 +1,5 @@
 <UserControl xmlns="https://github.com/avaloniaui"
-             xmlns:local="clr-namespace:ControlCatalog.Models;assembly=ControlCatalog"
+             xmlns:local="using:ControlCatalog.Models"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              x:Class="ControlCatalog.Pages.DataGridPage">
   <UserControl.Resources>
@@ -26,7 +26,8 @@
         <DataGrid Name="dataGrid1" Margin="12" CanUserResizeColumns="True" CanUserReorderColumns="True" CanUserSortColumns="True" HeadersVisibility="All">
           <DataGrid.Columns>
             <DataGridTextColumn Header="Country" Binding="{Binding Name}" Width="6*" />
-            <DataGridTextColumn Header="Region" Binding="{Binding Region}" Width="4*" />
+            <!-- CompiledBinding example of usage. -->
+            <DataGridTextColumn Header="Region" Binding="{CompiledBinding Region}" Width="4*" x:DataType="local:Country" />
             <DataGridTextColumn Header="Population" Binding="{Binding Population}" Width="3*" />
             <DataGridTextColumn Header="Area" Binding="{Binding Area}" Width="3*" />
             <DataGridTextColumn Header="GDP" Binding="{Binding GDP}" Width="3*" CellStyleClasses="gdp" />
diff --git a/samples/ControlCatalog/Pages/DataGridPage.xaml.cs b/samples/ControlCatalog/Pages/DataGridPage.xaml.cs
index 2a30f4d91b..dc5cc49a90 100644
--- a/samples/ControlCatalog/Pages/DataGridPage.xaml.cs
+++ b/samples/ControlCatalog/Pages/DataGridPage.xaml.cs
@@ -24,8 +24,10 @@ namespace ControlCatalog.Pages
             dg1.LoadingRow += Dg1_LoadingRow;
             dg1.Sorting += (s, a) =>
             {
-                var property = ((a.Column as DataGridBoundColumn)?.Binding as Binding).Path;
-                if (property == dataGridSortDescription.PropertyPath
+                var binding = (a.Column as DataGridBoundColumn)?.Binding as Binding;
+
+                if (binding?.Path is string property
+                    && property == dataGridSortDescription.PropertyPath
                     && !collectionView1.SortDescriptions.Contains(dataGridSortDescription))
                 {
                     collectionView1.SortDescriptions.Add(dataGridSortDescription);
diff --git a/src/Avalonia.Base/EnumExtensions.cs b/src/Avalonia.Base/EnumExtensions.cs
index 1e4864283f..bc1f8d36a9 100644
--- a/src/Avalonia.Base/EnumExtensions.cs
+++ b/src/Avalonia.Base/EnumExtensions.cs
@@ -11,10 +11,32 @@ namespace Avalonia
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static unsafe bool HasFlagCustom<T>(this T value, T flag) where T : unmanaged, Enum
         {
-            var intValue = *(int*)&value;
-            var intFlag = *(int*)&flag;
-
-            return (intValue & intFlag) == intFlag;
+            if (sizeof(T) == 1)
+            {
+                var byteValue = Unsafe.As<T, byte>(ref value);
+                var byteFlag = Unsafe.As<T, byte>(ref flag);
+                return (byteValue & byteFlag) == byteFlag;
+            }
+            else if (sizeof(T) == 2)
+            {
+                var shortValue = Unsafe.As<T, short>(ref value);
+                var shortFlag = Unsafe.As<T, short>(ref flag);
+                return (shortValue & shortFlag) == shortFlag;
+            }
+            else if (sizeof(T) == 4)
+            {
+                var intValue = Unsafe.As<T, int>(ref value);
+                var intFlag = Unsafe.As<T, int>(ref flag);
+                return (intValue & intFlag) == intFlag;
+            }
+            else if (sizeof(T) == 8)
+            {
+                var longValue = Unsafe.As<T, long>(ref value);
+                var longFlag = Unsafe.As<T, long>(ref flag);
+                return (longValue & longFlag) == longFlag;
+            }
+            else
+                throw new NotSupportedException("Enum with size of " + Unsafe.SizeOf<T>() + " are not supported");
         }
     }
 }
diff --git a/src/Avalonia.Base/Utilities/TypeUtilities.cs b/src/Avalonia.Base/Utilities/TypeUtilities.cs
index d0d88166a7..097731bc60 100644
--- a/src/Avalonia.Base/Utilities/TypeUtilities.cs
+++ b/src/Avalonia.Base/Utilities/TypeUtilities.cs
@@ -372,8 +372,8 @@ namespace Avalonia.Utilities
             const string implicitName = "op_Implicit";
             const string explicitName = "op_Explicit";
 
-            bool allowImplicit = (operatorType & OperatorType.Implicit) != 0;
-            bool allowExplicit = (operatorType & OperatorType.Explicit) != 0;
+            bool allowImplicit = operatorType.HasFlagCustom(OperatorType.Implicit);
+            bool allowExplicit = operatorType.HasFlagCustom(OperatorType.Explicit);
 
             foreach (MethodInfo method in fromType.GetMethods())
             {
diff --git a/src/Avalonia.Controls.DataGrid/Collections/DataGridCollectionView.cs b/src/Avalonia.Controls.DataGrid/Collections/DataGridCollectionView.cs
index 92734b128d..b97f2a2bcb 100644
--- a/src/Avalonia.Controls.DataGrid/Collections/DataGridCollectionView.cs
+++ b/src/Avalonia.Controls.DataGrid/Collections/DataGridCollectionView.cs
@@ -2595,7 +2595,7 @@ namespace Avalonia.Collections
         /// <returns>Whether the specified flag is set</returns>
         private bool CheckFlag(CollectionViewFlags flags)
         {
-            return (_flags & flags) != 0;
+            return _flags.HasFlagCustom(flags);
         }
 
         /// <summary>
diff --git a/src/Avalonia.Controls.DataGrid/DataGridBoundColumn.cs b/src/Avalonia.Controls.DataGrid/DataGridBoundColumn.cs
index 1e72a07760..90401a00a2 100644
--- a/src/Avalonia.Controls.DataGrid/DataGridBoundColumn.cs
+++ b/src/Avalonia.Controls.DataGrid/DataGridBoundColumn.cs
@@ -10,7 +10,8 @@ using System.Reactive.Disposables;
 using System.Reactive.Subjects;
 using Avalonia.Reactive;
 using System.Diagnostics;
-using Avalonia.Controls.Utils; 
+using Avalonia.Controls.Utils;
+using Avalonia.Markup.Xaml.MarkupExtensions;
 
 namespace Avalonia.Controls
 {
@@ -47,14 +48,15 @@ namespace Avalonia.Controls
 
                     if (_binding != null)
                     {
-                        if(_binding is Avalonia.Data.Binding binding)
+                        if(_binding is BindingBase binding)
                         {
                             if (binding.Mode == BindingMode.OneWayToSource)
                             {
                                 throw new InvalidOperationException("DataGridColumn doesn't support BindingMode.OneWayToSource. Use BindingMode.TwoWay instead.");
                             }
 
-                            if (!String.IsNullOrEmpty(binding.Path) && binding.Mode == BindingMode.Default)
+                            var path = (binding as Binding)?.Path ?? (binding as CompiledBindingExtension)?.Path.ToString();
+                            if (!string.IsNullOrEmpty(path) && binding.Mode == BindingMode.Default)
                             {
                                 binding.Mode = BindingMode.TwoWay;
                             } 
@@ -136,13 +138,16 @@ namespace Avalonia.Controls
         internal void SetHeaderFromBinding()
         {
             if (OwningGrid != null && OwningGrid.DataConnection.DataType != null
-                && Header == null && Binding != null && Binding is Binding binding
-                && !String.IsNullOrWhiteSpace(binding.Path))
+                && Header == null && Binding != null && Binding is BindingBase binding)
             {
-                string header = OwningGrid.DataConnection.DataType.GetDisplayName(binding.Path);
-                if (header != null)
+                var path = (binding as Binding)?.Path ?? (binding as CompiledBindingExtension)?.Path.ToString();
+                if (!string.IsNullOrWhiteSpace(path))
                 {
-                    Header = header;
+                    var header = OwningGrid.DataConnection.DataType.GetDisplayName(path);
+                    if (header != null)
+                    {
+                        Header = header;
+                    }
                 }
             }
         }
diff --git a/src/Avalonia.Controls.DataGrid/DataGridColumn.cs b/src/Avalonia.Controls.DataGrid/DataGridColumn.cs
index 92ddd4e736..407d6ff058 100644
--- a/src/Avalonia.Controls.DataGrid/DataGridColumn.cs
+++ b/src/Avalonia.Controls.DataGrid/DataGridColumn.cs
@@ -12,6 +12,7 @@ using System;
 using System.Linq;
 using System.Diagnostics;
 using Avalonia.Controls.Utils;
+using Avalonia.Markup.Xaml.MarkupExtensions;
 
 namespace Avalonia.Controls
 {
@@ -1033,13 +1034,16 @@ namespace Avalonia.Controls
 
             if (String.IsNullOrEmpty(result))
             {
-
-                if(this is DataGridBoundColumn boundColumn && 
-                    boundColumn.Binding != null &&
-                    boundColumn.Binding is Binding binding &&
-                    binding.Path != null)
+                if (this is DataGridBoundColumn boundColumn)
                 {
-                    result = binding.Path;
+                    if (boundColumn.Binding is Binding binding)
+                    {
+                        result = binding.Path;
+                    }
+                    else if (boundColumn.Binding is CompiledBindingExtension compiledBinding)
+                    {
+                        result = compiledBinding.Path.ToString();
+                    }
                 }
             }
 
diff --git a/src/Avalonia.Controls.DataGrid/DataGridColumns.cs b/src/Avalonia.Controls.DataGrid/DataGridColumns.cs
index 46bcd0d347..a4577ee952 100644
--- a/src/Avalonia.Controls.DataGrid/DataGridColumns.cs
+++ b/src/Avalonia.Controls.DataGrid/DataGridColumns.cs
@@ -5,6 +5,7 @@
 
 using Avalonia.Controls.Utils;
 using Avalonia.Data;
+using Avalonia.Markup.Xaml.MarkupExtensions;
 using Avalonia.Utilities;
 using System;
 using System.Collections.Generic;
@@ -141,9 +142,9 @@ namespace Avalonia.Controls
             Debug.Assert(dataGridColumn != null);
 
             if (dataGridColumn is DataGridBoundColumn dataGridBoundColumn && 
-                dataGridBoundColumn.Binding is Binding binding)
+                dataGridBoundColumn.Binding is BindingBase binding)
             {
-                string path = binding.Path;
+                var path = (binding as Binding)?.Path ?? (binding as CompiledBindingExtension)?.Path.ToString();
 
                 if (string.IsNullOrWhiteSpace(path))
                 {
diff --git a/src/Avalonia.Controls/ComboBox.cs b/src/Avalonia.Controls/ComboBox.cs
index 7f2acb58fe..20ca41bc57 100644
--- a/src/Avalonia.Controls/ComboBox.cs
+++ b/src/Avalonia.Controls/ComboBox.cs
@@ -188,7 +188,7 @@ namespace Avalonia.Controls
                 return;
 
             if (e.Key == Key.F4 ||
-                ((e.Key == Key.Down || e.Key == Key.Up) && ((e.KeyModifiers & KeyModifiers.Alt) != 0)))
+                ((e.Key == Key.Down || e.Key == Key.Up) && e.KeyModifiers.HasFlagCustom(KeyModifiers.Alt)))
             {
                 IsDropDownOpen = !IsDropDownOpen;
                 e.Handled = true;
diff --git a/src/Avalonia.Controls/ContextMenu.cs b/src/Avalonia.Controls/ContextMenu.cs
index fb8080f0d4..57e4909e39 100644
--- a/src/Avalonia.Controls/ContextMenu.cs
+++ b/src/Avalonia.Controls/ContextMenu.cs
@@ -269,7 +269,43 @@ namespace Avalonia.Controls
             }
 
             control ??= _attachedControls![0];
+            Open(control, PlacementTarget ?? control);
+        }
+
+        /// <summary>
+        /// Closes the menu.
+        /// </summary>
+        public override void Close()
+        {
+            if (!IsOpen)
+            {
+                return;
+            }
 
+            if (_popup != null && _popup.IsVisible)
+            {
+                _popup.IsOpen = false;
+            }
+        }
+
+        void ISetterValue.Initialize(ISetter setter)
+        {
+            // ContextMenu can be assigned to the ContextMenu property in a setter. This overrides
+            // the behavior defined in Control which requires controls to be wrapped in a <template>.
+            if (!(setter is Setter s && s.Property == ContextMenuProperty))
+            {
+                throw new InvalidOperationException(
+                    "Cannot use a control as a Setter value. Wrap the control in a <Template>.");
+            }
+        }
+
+        protected override IItemContainerGenerator CreateItemContainerGenerator()
+        {
+            return new MenuItemContainerGenerator(this);
+        }
+
+        private void Open(Control control, Control placementTarget)
+        {
             if (IsOpen)
             {
                 return;
@@ -286,7 +322,6 @@ namespace Avalonia.Controls
                     PlacementGravity = PlacementGravity,
                     PlacementMode = PlacementMode,
                     PlacementRect = PlacementRect,
-                    PlacementTarget = PlacementTarget ?? control,
                     IsLightDismissEnabled = true,
                     OverlayDismissEventPassThrough = true,
                     WindowManagerAddShadowHint = WindowManagerAddShadowHint,
@@ -302,11 +337,7 @@ namespace Avalonia.Controls
                 ((ISetLogicalParent)_popup).SetParent(control);
             }
 
-            if (PlacementTarget is null && _popup.PlacementTarget != control)
-            {
-                _popup.PlacementTarget = control;
-            }
-
+            _popup.PlacementTarget = placementTarget;
             _popup.Child = this;
             IsOpen = true;
             _popup.IsOpen = true;
@@ -318,38 +349,6 @@ namespace Avalonia.Controls
             });
         }
 
-        /// <summary>
-        /// Closes the menu.
-        /// </summary>
-        public override void Close()
-        {
-            if (!IsOpen)
-            {
-                return;
-            }
-
-            if (_popup != null && _popup.IsVisible)
-            {
-                _popup.IsOpen = false;
-            }
-        }
-
-        void ISetterValue.Initialize(ISetter setter)
-        {
-            // ContextMenu can be assigned to the ContextMenu property in a setter. This overrides
-            // the behavior defined in Control which requires controls to be wrapped in a <template>.
-            if (!(setter is Setter s && s.Property == ContextMenuProperty))
-            {
-                throw new InvalidOperationException(
-                    "Cannot use a control as a Setter value. Wrap the control in a <Template>.");
-            }
-        }
-
-        protected override IItemContainerGenerator CreateItemContainerGenerator()
-        {
-            return new MenuItemContainerGenerator(this);
-        }
-
         private void PopupOpened(object sender, EventArgs e)
         {
             _previousFocus = FocusManager.Instance?.Current;
@@ -403,7 +402,7 @@ namespace Avalonia.Controls
                 if (contextMenu.CancelOpening())
                     return;
 
-                contextMenu.Open(control);
+                contextMenu.Open(control, e.Source as Control ?? control);
                 e.Handled = true;
             }
         }
diff --git a/src/Avalonia.Controls/Grid.cs b/src/Avalonia.Controls/Grid.cs
index 6357ec98a8..66266c3b61 100644
--- a/src/Avalonia.Controls/Grid.cs
+++ b/src/Avalonia.Controls/Grid.cs
@@ -637,7 +637,7 @@ namespace Avalonia.Controls
         /// </summary>
         internal bool MeasureOverrideInProgress
         {
-            get { return (CheckFlagsAnd(Flags.MeasureOverrideInProgress)); }
+            get { return CheckFlags(Flags.MeasureOverrideInProgress); }
             set { SetFlags(value, Flags.MeasureOverrideInProgress); }
         }
 
@@ -646,7 +646,7 @@ namespace Avalonia.Controls
         /// </summary>
         internal bool ArrangeOverrideInProgress
         {
-            get { return (CheckFlagsAnd(Flags.ArrangeOverrideInProgress)); }
+            get { return CheckFlags(Flags.ArrangeOverrideInProgress); }
             set { SetFlags(value, Flags.ArrangeOverrideInProgress); }
         }
 
@@ -2350,25 +2350,12 @@ namespace Avalonia.Controls
         }
 
         /// <summary>
-        /// CheckFlagsAnd returns <c>true</c> if all the flags in the
+        /// CheckFlags returns <c>true</c> if all the flags in the
         /// given bitmask are set on the object.
         /// </summary>
-        private bool CheckFlagsAnd(Flags flags)
+        private bool CheckFlags(Flags flags)
         {
-            return ((_flags & flags) == flags);
-        }
-
-        /// <summary>
-        /// CheckFlagsOr returns <c>true</c> if at least one flag in the
-        /// given bitmask is set.
-        /// </summary>
-        /// <remarks>
-        /// If no bits are set in the given bitmask, the method returns
-        /// <c>true</c>.
-        /// </remarks>
-        private bool CheckFlagsOr(Flags flags)
-        {
-            return (flags == 0 || (_flags & flags) != 0);
+            return _flags.HasFlagCustom(flags);
         }
 
         private static void OnShowGridLinesPropertyChanged(AvaloniaObject d, AvaloniaPropertyChangedEventArgs e)
@@ -2535,7 +2522,7 @@ namespace Avalonia.Controls
         /// </summary>
         private bool CellsStructureDirty
         {
-            get { return (!CheckFlagsAnd(Flags.ValidCellsStructure)); }
+            get { return !CheckFlags(Flags.ValidCellsStructure); }
             set { SetFlags(!value, Flags.ValidCellsStructure); }
         }
 
@@ -2544,7 +2531,7 @@ namespace Avalonia.Controls
         /// </summary>
         private bool ListenToNotifications
         {
-            get { return (CheckFlagsAnd(Flags.ListenToNotifications)); }
+            get { return CheckFlags(Flags.ListenToNotifications); }
             set { SetFlags(value, Flags.ListenToNotifications); }
         }
 
@@ -2553,7 +2540,7 @@ namespace Avalonia.Controls
         /// </summary>
         private bool SizeToContentU
         {
-            get { return (CheckFlagsAnd(Flags.SizeToContentU)); }
+            get { return CheckFlags(Flags.SizeToContentU); }
             set { SetFlags(value, Flags.SizeToContentU); }
         }
 
@@ -2562,7 +2549,7 @@ namespace Avalonia.Controls
         /// </summary>
         private bool SizeToContentV
         {
-            get { return (CheckFlagsAnd(Flags.SizeToContentV)); }
+            get { return CheckFlags(Flags.SizeToContentV); }
             set { SetFlags(value, Flags.SizeToContentV); }
         }
 
@@ -2571,7 +2558,7 @@ namespace Avalonia.Controls
         /// </summary>
         private bool HasStarCellsU
         {
-            get { return (CheckFlagsAnd(Flags.HasStarCellsU)); }
+            get { return CheckFlags(Flags.HasStarCellsU); }
             set { SetFlags(value, Flags.HasStarCellsU); }
         }
 
@@ -2580,7 +2567,7 @@ namespace Avalonia.Controls
         /// </summary>
         private bool HasStarCellsV
         {
-            get { return (CheckFlagsAnd(Flags.HasStarCellsV)); }
+            get { return CheckFlags(Flags.HasStarCellsV); }
             set { SetFlags(value, Flags.HasStarCellsV); }
         }
 
@@ -2589,7 +2576,7 @@ namespace Avalonia.Controls
         /// </summary>
         private bool HasGroup3CellsInAutoRows
         {
-            get { return (CheckFlagsAnd(Flags.HasGroup3CellsInAutoRows)); }
+            get { return CheckFlags(Flags.HasGroup3CellsInAutoRows); }
             set { SetFlags(value, Flags.HasGroup3CellsInAutoRows); }
         }
 
@@ -2803,10 +2790,10 @@ namespace Avalonia.Controls
             internal LayoutTimeSizeType SizeTypeU;
             internal LayoutTimeSizeType SizeTypeV;
             internal int Next;
-            internal bool IsStarU { get { return ((SizeTypeU & LayoutTimeSizeType.Star) != 0); } }
-            internal bool IsAutoU { get { return ((SizeTypeU & LayoutTimeSizeType.Auto) != 0); } }
-            internal bool IsStarV { get { return ((SizeTypeV & LayoutTimeSizeType.Star) != 0); } }
-            internal bool IsAutoV { get { return ((SizeTypeV & LayoutTimeSizeType.Auto) != 0); } }
+            internal bool IsStarU => SizeTypeU.HasFlagCustom(LayoutTimeSizeType.Star);
+            internal bool IsAutoU => SizeTypeU.HasFlagCustom(LayoutTimeSizeType.Auto);
+            internal bool IsStarV => SizeTypeV.HasFlagCustom(LayoutTimeSizeType.Star);
+            internal bool IsAutoV => SizeTypeV.HasFlagCustom(LayoutTimeSizeType.Auto);
         }
 
         /// <summary>
diff --git a/src/Avalonia.Controls/ListBox.cs b/src/Avalonia.Controls/ListBox.cs
index d1b8038581..b6b3cc786c 100644
--- a/src/Avalonia.Controls/ListBox.cs
+++ b/src/Avalonia.Controls/ListBox.cs
@@ -135,8 +135,8 @@ namespace Avalonia.Controls
                 e.Handled = UpdateSelectionFromEventSource(
                     e.Source,
                     true,
-                    (e.KeyModifiers & KeyModifiers.Shift) != 0,
-                    (e.KeyModifiers & KeyModifiers.Control) != 0);
+                    e.KeyModifiers.HasFlagCustom(KeyModifiers.Shift),
+                    e.KeyModifiers.HasFlagCustom(KeyModifiers.Control));
             }
         }
 
@@ -154,8 +154,8 @@ namespace Avalonia.Controls
                     e.Handled = UpdateSelectionFromEventSource(
                         e.Source,
                         true,
-                        (e.KeyModifiers & KeyModifiers.Shift) != 0,
-                        (e.KeyModifiers & KeyModifiers.Control) != 0,
+                        e.KeyModifiers.HasFlagCustom(KeyModifiers.Shift),
+                        e.KeyModifiers.HasFlagCustom(KeyModifiers.Control),
                         point.Properties.IsRightButtonPressed);
                 }
             }
diff --git a/src/Avalonia.Controls/Platform/InProcessDragSource.cs b/src/Avalonia.Controls/Platform/InProcessDragSource.cs
index 9d644aaa00..7e1a7378c7 100644
--- a/src/Avalonia.Controls/Platform/InProcessDragSource.cs
+++ b/src/Avalonia.Controls/Platform/InProcessDragSource.cs
@@ -73,20 +73,20 @@ namespace Avalonia.Platform
         {
             if (effect == DragDropEffects.Copy || effect == DragDropEffects.Move || effect == DragDropEffects.Link || effect == DragDropEffects.None)
                 return effect; // No need to check for the modifiers.
-            if (effect.HasFlag(DragDropEffects.Link) && modifiers.HasFlag(RawInputModifiers.Alt))
+            if (effect.HasFlagCustom(DragDropEffects.Link) && modifiers.HasFlagCustom(RawInputModifiers.Alt))
                 return DragDropEffects.Link;
-            if (effect.HasFlag(DragDropEffects.Copy) && modifiers.HasFlag(RawInputModifiers.Control))
+            if (effect.HasFlagCustom(DragDropEffects.Copy) && modifiers.HasFlagCustom(RawInputModifiers.Control))
                 return DragDropEffects.Copy;
             return DragDropEffects.Move;
         }
 
         private StandardCursorType GetCursorForDropEffect(DragDropEffects effects)
         {
-            if (effects.HasFlag(DragDropEffects.Copy))
+            if (effects.HasFlagCustom(DragDropEffects.Copy))
                 return StandardCursorType.DragCopy;
-            if (effects.HasFlag(DragDropEffects.Move))
+            if (effects.HasFlagCustom(DragDropEffects.Move))
                 return StandardCursorType.DragMove;
-            if (effects.HasFlag(DragDropEffects.Link))
+            if (effects.HasFlagCustom(DragDropEffects.Link))
                 return StandardCursorType.DragLink;
             return StandardCursorType.No;
         }
@@ -161,7 +161,7 @@ namespace Avalonia.Platform
             
             void CheckDraggingAccepted(RawInputModifiers changedMouseButton)
             {
-                if (_initialInputModifiers.Value.HasFlag(changedMouseButton))
+                if (_initialInputModifiers.Value.HasFlagCustom(changedMouseButton))
                 {
                     var result = RaiseEventAndUpdateCursor(RawDragEventType.Drop, e.Root, e.Position, e.InputModifiers);
                     UpdateCursor(null, DragDropEffects.None);
diff --git a/src/Avalonia.Controls/Primitives/PopupPositioning/IPopupPositioner.cs b/src/Avalonia.Controls/Primitives/PopupPositioning/IPopupPositioner.cs
index aed7dff0fe..545034239f 100644
--- a/src/Avalonia.Controls/Primitives/PopupPositioning/IPopupPositioner.cs
+++ b/src/Avalonia.Controls/Primitives/PopupPositioning/IPopupPositioner.cs
@@ -253,9 +253,8 @@ namespace Avalonia.Controls.Primitives.PopupPositioning
     {
         public static void ValidateEdge(this PopupAnchor edge)
         {
-            if (((edge & PopupAnchor.Left) != 0 && (edge & PopupAnchor.Right) != 0)
-                ||
-                ((edge & PopupAnchor.Top) != 0 && (edge & PopupAnchor.Bottom) != 0))
+            if (edge.HasFlagCustom(PopupAnchor.Left) && edge.HasFlagCustom(PopupAnchor.Right) ||
+                edge.HasFlagCustom(PopupAnchor.Top) && edge.HasFlagCustom(PopupAnchor.Bottom))
                 throw new ArgumentException("Opposite edges specified");
         }
 
@@ -266,25 +265,25 @@ namespace Avalonia.Controls.Primitives.PopupPositioning
 
         public static PopupAnchor Flip(this PopupAnchor edge)
         {
-            var hmask = PopupAnchor.Left | PopupAnchor.Right;
-            var vmask = PopupAnchor.Top | PopupAnchor.Bottom;
-            if ((edge & hmask) != 0)
-                edge ^= hmask;
-            if ((edge & vmask) != 0)
-                edge ^= vmask;
+            if (edge.HasFlagCustom(PopupAnchor.HorizontalMask))
+                edge ^= PopupAnchor.HorizontalMask;
+
+            if (edge.HasFlagCustom(PopupAnchor.VerticalMask))
+                edge ^= PopupAnchor.VerticalMask;
+
             return edge;
         }
 
         public static PopupAnchor FlipX(this PopupAnchor edge)
         {
-            if ((edge & PopupAnchor.HorizontalMask) != 0)
+            if (edge.HasFlagCustom(PopupAnchor.HorizontalMask))
                 edge ^= PopupAnchor.HorizontalMask;
             return edge;
         }
         
         public static PopupAnchor FlipY(this PopupAnchor edge)
         {
-            if ((edge & PopupAnchor.VerticalMask) != 0)
+            if (edge.HasFlagCustom(PopupAnchor.VerticalMask))
                 edge ^= PopupAnchor.VerticalMask;
             return edge;
         }
diff --git a/src/Avalonia.Controls/Primitives/PopupPositioning/ManagedPopupPositioner.cs b/src/Avalonia.Controls/Primitives/PopupPositioning/ManagedPopupPositioner.cs
index 7f1dbdf592..80b32b5ef8 100644
--- a/src/Avalonia.Controls/Primitives/PopupPositioning/ManagedPopupPositioner.cs
+++ b/src/Avalonia.Controls/Primitives/PopupPositioning/ManagedPopupPositioner.cs
@@ -42,16 +42,16 @@ namespace Avalonia.Controls.Primitives.PopupPositioning
         private static Point GetAnchorPoint(Rect anchorRect, PopupAnchor edge)
         {
             double x, y;
-            if ((edge & PopupAnchor.Left) != 0)
+            if (edge.HasFlagCustom(PopupAnchor.Left))
                 x = anchorRect.X;
-            else if ((edge & PopupAnchor.Right) != 0)
+            else if (edge.HasFlagCustom(PopupAnchor.Right))
                 x = anchorRect.Right;
             else
                 x = anchorRect.X + anchorRect.Width / 2;
             
-            if ((edge & PopupAnchor.Top) != 0)
+            if (edge.HasFlagCustom(PopupAnchor.Top))
                 y = anchorRect.Y;
-            else if ((edge & PopupAnchor.Bottom) != 0)
+            else if (edge.HasFlagCustom(PopupAnchor.Bottom))
                 y = anchorRect.Bottom;
             else
                 y = anchorRect.Y + anchorRect.Height / 2;
@@ -61,16 +61,16 @@ namespace Avalonia.Controls.Primitives.PopupPositioning
         private static Point Gravitate(Point anchorPoint, Size size, PopupGravity gravity)
         {
             double x, y;
-            if ((gravity & PopupGravity.Left) != 0)
+            if (gravity.HasFlagCustom(PopupGravity.Left))
                 x = -size.Width;
-            else if ((gravity & PopupGravity.Right) != 0)
+            else if (gravity.HasFlagCustom(PopupGravity.Right))
                 x = 0;
             else
                 x = -size.Width / 2;
             
-            if ((gravity & PopupGravity.Top) != 0)
+            if (gravity.HasFlagCustom(PopupGravity.Top))
                 y = -size.Height;
-            else if ((gravity & PopupGravity.Bottom) != 0)
+            else if (gravity.HasFlagCustom(PopupGravity.Bottom))
                 y = 0;
             else
                 y = -size.Height / 2;
@@ -125,21 +125,13 @@ namespace Avalonia.Controls.Primitives.PopupPositioning
 
             bool FitsInBounds(Rect rc, PopupAnchor edge = PopupAnchor.AllMask)
             {
-                if ((edge & PopupAnchor.Left) != 0
-                    && rc.X < bounds.X)
-                    return false;
-
-                if ((edge & PopupAnchor.Top) != 0
-                    && rc.Y < bounds.Y)
-                    return false;
-
-                if ((edge & PopupAnchor.Right) != 0
-                    && rc.Right > bounds.Right)
-                    return false;
-
-                if ((edge & PopupAnchor.Bottom) != 0
-                    && rc.Bottom > bounds.Bottom)
+                if (edge.HasFlagCustom(PopupAnchor.Left) && rc.X < bounds.X ||
+                    edge.HasFlagCustom(PopupAnchor.Top) && rc.Y < bounds.Y ||
+                    edge.HasFlagCustom(PopupAnchor.Right) && rc.Right > bounds.Right ||
+                    edge.HasFlagCustom(PopupAnchor.Bottom) && rc.Bottom > bounds.Bottom)
+                {
                     return false;
+                }
 
                 return true;
             }
@@ -155,7 +147,7 @@ namespace Avalonia.Controls.Primitives.PopupPositioning
             // If flipping geometry and anchor is allowed and helps, use the flipped one,
             // otherwise leave it as is
             if (!FitsInBounds(geo, PopupAnchor.HorizontalMask)
-                && (constraintAdjustment & PopupPositionerConstraintAdjustment.FlipX) != 0)
+                && constraintAdjustment.HasFlagCustom(PopupPositionerConstraintAdjustment.FlipX))
             {
                 var flipped = GetUnconstrained(anchor.FlipX(), gravity.FlipX());
                 if (FitsInBounds(flipped, PopupAnchor.HorizontalMask))
@@ -163,7 +155,7 @@ namespace Avalonia.Controls.Primitives.PopupPositioning
             }
 
             // If sliding is allowed, try moving the rect into the bounds
-            if ((constraintAdjustment & PopupPositionerConstraintAdjustment.SlideX) != 0)
+            if (constraintAdjustment.HasFlagCustom(PopupPositionerConstraintAdjustment.SlideX))
             {
                 geo = geo.WithX(Math.Max(geo.X, bounds.X));
                 if (geo.Right > bounds.Right)
@@ -171,7 +163,7 @@ namespace Avalonia.Controls.Primitives.PopupPositioning
             }
             
             // Resize the rect horizontally if allowed.
-            if ((constraintAdjustment & PopupPositionerConstraintAdjustment.ResizeX) != 0)
+            if (constraintAdjustment.HasFlagCustom(PopupPositionerConstraintAdjustment.ResizeX))
             {
                 var unconstrainedRect = geo;
 
@@ -194,7 +186,7 @@ namespace Avalonia.Controls.Primitives.PopupPositioning
             // If flipping geometry and anchor is allowed and helps, use the flipped one,
             // otherwise leave it as is
             if (!FitsInBounds(geo, PopupAnchor.VerticalMask)
-                && (constraintAdjustment & PopupPositionerConstraintAdjustment.FlipY) != 0)
+                && constraintAdjustment.HasFlagCustom(PopupPositionerConstraintAdjustment.FlipY))
             {
                 var flipped = GetUnconstrained(anchor.FlipY(), gravity.FlipY());
                 if (FitsInBounds(flipped, PopupAnchor.VerticalMask))
@@ -202,7 +194,7 @@ namespace Avalonia.Controls.Primitives.PopupPositioning
             }
 
             // If sliding is allowed, try moving the rect into the bounds
-            if ((constraintAdjustment & PopupPositionerConstraintAdjustment.SlideY) != 0)
+            if (constraintAdjustment.HasFlagCustom(PopupPositionerConstraintAdjustment.SlideY))
             {
                 geo = geo.WithY(Math.Max(geo.Y, bounds.Y));
                 if (geo.Bottom > bounds.Bottom)
@@ -210,7 +202,7 @@ namespace Avalonia.Controls.Primitives.PopupPositioning
             }
 
             // Resize the rect vertically if allowed.
-            if ((constraintAdjustment & PopupPositionerConstraintAdjustment.ResizeY) != 0)
+            if (constraintAdjustment.HasFlagCustom(PopupPositionerConstraintAdjustment.ResizeY))
             {
                 var unconstrainedRect = geo;
 
diff --git a/src/Avalonia.Controls/Primitives/SelectingItemsControl.cs b/src/Avalonia.Controls/Primitives/SelectingItemsControl.cs
index 280f46be9f..2cd69793dc 100644
--- a/src/Avalonia.Controls/Primitives/SelectingItemsControl.cs
+++ b/src/Avalonia.Controls/Primitives/SelectingItemsControl.cs
@@ -321,7 +321,7 @@ namespace Avalonia.Controls.Primitives
         /// <summary>
         /// Gets a value indicating whether <see cref="SelectionMode.AlwaysSelected"/> is set.
         /// </summary>
-        protected bool AlwaysSelected => (SelectionMode & SelectionMode.AlwaysSelected) != 0;
+        protected bool AlwaysSelected => SelectionMode.HasFlagCustom(SelectionMode.AlwaysSelected);
 
         /// <inheritdoc/>
         public override void BeginInit()
@@ -487,7 +487,7 @@ namespace Avalonia.Controls.Primitives
 
                 if (ItemCount > 0 &&
                     Match(keymap.SelectAll) &&
-                    SelectionMode.HasFlag(SelectionMode.Multiple))
+                    SelectionMode.HasFlagCustom(SelectionMode.Multiple))
                 {
                     Selection.SelectAll();
                     e.Handled = true;
@@ -577,8 +577,8 @@ namespace Avalonia.Controls.Primitives
             }
 
             var mode = SelectionMode;
-            var multi = (mode & SelectionMode.Multiple) != 0;
-            var toggle = (toggleModifier || (mode & SelectionMode.Toggle) != 0);
+            var multi = mode.HasFlagCustom(SelectionMode.Multiple);
+            var toggle = toggleModifier || mode.HasFlagCustom(SelectionMode.Toggle);
             var range = multi && rangeModifier;
 
             if (!select)
diff --git a/src/Avalonia.Controls/Repeater/RepeaterLayoutContext.cs b/src/Avalonia.Controls/Repeater/RepeaterLayoutContext.cs
index fd33eeaf39..4eadced423 100644
--- a/src/Avalonia.Controls/Repeater/RepeaterLayoutContext.cs
+++ b/src/Avalonia.Controls/Repeater/RepeaterLayoutContext.cs
@@ -53,8 +53,8 @@ namespace Avalonia.Controls
         {
             return _owner.GetElementImpl(
                 index,
-                (options & ElementRealizationOptions.ForceCreate) != 0,
-                (options & ElementRealizationOptions.SuppressAutoRecycle) != 0);
+                options.HasFlagCustom(ElementRealizationOptions.ForceCreate),
+                options.HasFlagCustom(ElementRealizationOptions.SuppressAutoRecycle));
         }
 
         protected override object GetItemAtCore(int index) => _owner.ItemsSourceView.GetAt(index);
diff --git a/src/Avalonia.Controls/TextBox.cs b/src/Avalonia.Controls/TextBox.cs
index 90064fad57..54d3af9b59 100644
--- a/src/Avalonia.Controls/TextBox.cs
+++ b/src/Avalonia.Controls/TextBox.cs
@@ -585,7 +585,7 @@ namespace Avalonia.Controls
             var keymap = AvaloniaLocator.Current.GetService<PlatformHotkeyConfiguration>();
 
             bool Match(List<KeyGesture> gestures) => gestures.Any(g => g.Matches(e));
-            bool DetectSelection() => e.KeyModifiers.HasFlag(keymap.SelectionModifiers);
+            bool DetectSelection() => e.KeyModifiers.HasFlagCustom(keymap.SelectionModifiers);
 
             if (Match(keymap.SelectAll))
             {
@@ -703,7 +703,7 @@ namespace Avalonia.Controls
             }
             else
             {
-                bool hasWholeWordModifiers = modifiers.HasFlag(keymap.WholeWordTextActionModifiers);
+                bool hasWholeWordModifiers = modifiers.HasFlagCustom(keymap.WholeWordTextActionModifiers);
                 switch (e.Key)
                 {
                     case Key.Left:
diff --git a/src/Avalonia.Controls/TreeView.cs b/src/Avalonia.Controls/TreeView.cs
index 09742412d9..c8150cc200 100644
--- a/src/Avalonia.Controls/TreeView.cs
+++ b/src/Avalonia.Controls/TreeView.cs
@@ -412,7 +412,7 @@ namespace Avalonia.Controls
                 e.Handled = UpdateSelectionFromEventSource(
                     e.Source,
                     true,
-                    (e.KeyModifiers & KeyModifiers.Shift) != 0);
+                    e.KeyModifiers.HasFlagCustom(KeyModifiers.Shift));
             }
         }
 
@@ -521,8 +521,8 @@ namespace Avalonia.Controls
                     e.Handled = UpdateSelectionFromEventSource(
                         e.Source,
                         true,
-                        (e.KeyModifiers & KeyModifiers.Shift) != 0,
-                        (e.KeyModifiers & KeyModifiers.Control) != 0,
+                        e.KeyModifiers.HasFlagCustom(KeyModifiers.Shift),
+                        e.KeyModifiers.HasFlagCustom(KeyModifiers.Control),
                         point.Properties.IsRightButtonPressed);
                 }
             }
@@ -558,9 +558,9 @@ namespace Avalonia.Controls
             }
 
             var mode = SelectionMode;
-            var toggle = toggleModifier || (mode & SelectionMode.Toggle) != 0;
-            var multi = (mode & SelectionMode.Multiple) != 0;
-            var range = multi && selectedContainer != null && rangeModifier;
+            var toggle = toggleModifier || mode.HasFlagCustom(SelectionMode.Toggle);
+            var multi = mode.HasFlagCustom(SelectionMode.Multiple);
+            var range = multi && rangeModifier && selectedContainer != null;
 
             if (rightButton)
             {
diff --git a/src/Avalonia.FreeDesktop/DBusMenuExporter.cs b/src/Avalonia.FreeDesktop/DBusMenuExporter.cs
index e93ca64d3a..2cf533195e 100644
--- a/src/Avalonia.FreeDesktop/DBusMenuExporter.cs
+++ b/src/Avalonia.FreeDesktop/DBusMenuExporter.cs
@@ -223,13 +223,13 @@ namespace Avalonia.FreeDesktop
                             return null;
                         var lst = new List<string>();
                         var mod = item.Gesture;
-                        if ((mod.KeyModifiers & KeyModifiers.Control) != 0)
+                        if (mod.KeyModifiers.HasFlagCustom(KeyModifiers.Control))
                             lst.Add("Control");
-                        if ((mod.KeyModifiers & KeyModifiers.Alt) != 0)
+                        if (mod.KeyModifiers.HasFlagCustom(KeyModifiers.Alt))
                             lst.Add("Alt");
-                        if ((mod.KeyModifiers & KeyModifiers.Shift) != 0)
+                        if (mod.KeyModifiers.HasFlagCustom(KeyModifiers.Shift))
                             lst.Add("Shift");
-                        if ((mod.KeyModifiers & KeyModifiers.Meta) != 0)
+                        if (mod.KeyModifiers.HasFlagCustom(KeyModifiers.Meta))
                             lst.Add("Super");
                         lst.Add(item.Gesture.Key.ToString());
                         return new[] { lst.ToArray() };
diff --git a/src/Avalonia.Headless.Vnc/HeadlessVncFramebufferSource.cs b/src/Avalonia.Headless.Vnc/HeadlessVncFramebufferSource.cs
index 32f9f99709..fb61f25cea 100644
--- a/src/Avalonia.Headless.Vnc/HeadlessVncFramebufferSource.cs
+++ b/src/Avalonia.Headless.Vnc/HeadlessVncFramebufferSource.cs
@@ -33,11 +33,11 @@ namespace Avalonia.Headless.Vnc
                 {
                     Window?.MouseMove(pt);
                     foreach (var btn in CheckedButtons)
-                        if (_previousButtons.HasFlag(btn) && !buttons.HasFlag(btn))
+                        if (_previousButtons.HasFlagCustom(btn) && !buttons.HasFlagCustom(btn))
                             Window?.MouseUp(pt, TranslateButton(btn), modifiers);
                     
                     foreach (var btn in CheckedButtons)
-                        if (!_previousButtons.HasFlag(btn) && buttons.HasFlag(btn))
+                        if (!_previousButtons.HasFlagCustom(btn) && buttons.HasFlagCustom(btn))
                             Window?.MouseDown(pt, TranslateButton(btn), modifiers);
                     _previousButtons = buttons;
                 }, DispatcherPriority.Input);
diff --git a/src/Avalonia.Input/AccessKeyHandler.cs b/src/Avalonia.Input/AccessKeyHandler.cs
index 660584e2ed..731a409090 100644
--- a/src/Avalonia.Input/AccessKeyHandler.cs
+++ b/src/Avalonia.Input/AccessKeyHandler.cs
@@ -177,7 +177,7 @@ namespace Avalonia.Input
         {
             bool menuIsOpen = MainMenu?.IsOpen == true;
 
-            if ((e.KeyModifiers & KeyModifiers.Alt) != 0 || menuIsOpen)
+            if (e.KeyModifiers.HasFlagCustom(KeyModifiers.Alt) || menuIsOpen)
             {
                 // If any other key is pressed with the Alt key held down, or the main menu is open,
                 // find all controls who have registered that access key.
diff --git a/src/Avalonia.Input/FocusManager.cs b/src/Avalonia.Input/FocusManager.cs
index a1f1478f51..474b212a21 100644
--- a/src/Avalonia.Input/FocusManager.cs
+++ b/src/Avalonia.Input/FocusManager.cs
@@ -75,7 +75,9 @@ namespace Avalonia.Input
                 // If control is null, set focus to the topmost focus scope.
                 foreach (var scope in GetFocusScopeAncestors(Current).Reverse().ToList())
                 {
-                    if (_focusScopes.TryGetValue(scope, out var element) && element != null)
+                    if (scope != Scope &&
+                        _focusScopes.TryGetValue(scope, out var element) &&
+                        element != null)
                     {
                         Focus(element, method);
                         return;
diff --git a/src/Avalonia.ReactiveUI/AutoDataTemplateBindingHook.cs b/src/Avalonia.ReactiveUI/AutoDataTemplateBindingHook.cs
index fe4e9dd94a..b6cdb77f81 100644
--- a/src/Avalonia.ReactiveUI/AutoDataTemplateBindingHook.cs
+++ b/src/Avalonia.ReactiveUI/AutoDataTemplateBindingHook.cs
@@ -29,7 +29,7 @@ namespace Avalonia.ReactiveUI
 
         /// <inheritdoc/>
         public bool ExecuteHook(
-            object source, object target,
+            object? source, object target,
             Func<IObservedChange<object, object>[]> getCurrentViewModelProperties,
             Func<IObservedChange<object, object>[]> getCurrentViewProperties,
             BindingDirection direction)
diff --git a/src/Avalonia.ReactiveUI/Avalonia.ReactiveUI.csproj b/src/Avalonia.ReactiveUI/Avalonia.ReactiveUI.csproj
index 624c5772a9..2792ae1c91 100644
--- a/src/Avalonia.ReactiveUI/Avalonia.ReactiveUI.csproj
+++ b/src/Avalonia.ReactiveUI/Avalonia.ReactiveUI.csproj
@@ -3,6 +3,8 @@
     <TargetFramework>netstandard2.0</TargetFramework>
     <PackageId>Avalonia.ReactiveUI</PackageId>
     <SignAssembly>false</SignAssembly>
+    <Nullable>enable</Nullable>
+    <WarningsAsErrors>nullable</WarningsAsErrors>
   </PropertyGroup>
   <ItemGroup>
     <ProjectReference Include="..\..\packages\Avalonia\Avalonia.csproj" />
diff --git a/src/Avalonia.ReactiveUI/ReactiveUserControl.cs b/src/Avalonia.ReactiveUI/ReactiveUserControl.cs
index f4824ade0a..4987349162 100644
--- a/src/Avalonia.ReactiveUI/ReactiveUserControl.cs
+++ b/src/Avalonia.ReactiveUI/ReactiveUserControl.cs
@@ -17,8 +17,8 @@ namespace Avalonia.ReactiveUI
     /// <typeparam name="TViewModel">ViewModel type.</typeparam>
     public class ReactiveUserControl<TViewModel> : UserControl, IViewFor<TViewModel> where TViewModel : class
     {
-        public static readonly StyledProperty<TViewModel> ViewModelProperty = AvaloniaProperty
-            .Register<ReactiveUserControl<TViewModel>, TViewModel>(nameof(ViewModel));
+        public static readonly StyledProperty<TViewModel?> ViewModelProperty = AvaloniaProperty
+            .Register<ReactiveUserControl<TViewModel>, TViewModel?>(nameof(ViewModel));
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ReactiveUserControl{TViewModel}"/> class.
@@ -34,16 +34,16 @@ namespace Avalonia.ReactiveUI
         /// <summary>
         /// The ViewModel.
         /// </summary>
-        public TViewModel ViewModel
+        public TViewModel? ViewModel
         {
             get => GetValue(ViewModelProperty);
             set => SetValue(ViewModelProperty, value);
         }
 
-        object IViewFor.ViewModel
+        object? IViewFor.ViewModel
         {
             get => ViewModel;
-            set => ViewModel = (TViewModel)value;
+            set => ViewModel = (TViewModel?)value;
         }
 
         protected override void OnDataContextChanged(EventArgs e)
@@ -51,7 +51,7 @@ namespace Avalonia.ReactiveUI
             ViewModel = DataContext as TViewModel;
         }
 
-        private void OnViewModelChanged(object value)
+        private void OnViewModelChanged(object? value)
         {
             if (value == null)
             {
diff --git a/src/Avalonia.ReactiveUI/ReactiveWindow.cs b/src/Avalonia.ReactiveUI/ReactiveWindow.cs
index 758a807bfc..726fb3d661 100644
--- a/src/Avalonia.ReactiveUI/ReactiveWindow.cs
+++ b/src/Avalonia.ReactiveUI/ReactiveWindow.cs
@@ -17,8 +17,8 @@ namespace Avalonia.ReactiveUI
     /// <typeparam name="TViewModel">ViewModel type.</typeparam>
     public class ReactiveWindow<TViewModel> : Window, IViewFor<TViewModel> where TViewModel : class
     {
-        public static readonly StyledProperty<TViewModel> ViewModelProperty = AvaloniaProperty
-            .Register<ReactiveWindow<TViewModel>, TViewModel>(nameof(ViewModel));
+        public static readonly StyledProperty<TViewModel?> ViewModelProperty = AvaloniaProperty
+            .Register<ReactiveWindow<TViewModel>, TViewModel?>(nameof(ViewModel));
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ReactiveWindow{TViewModel}"/> class.
@@ -35,19 +35,19 @@ namespace Avalonia.ReactiveUI
         /// <summary>
         /// The ViewModel.
         /// </summary>
-        public TViewModel ViewModel
+        public TViewModel? ViewModel
         {
             get => GetValue(ViewModelProperty);
             set => SetValue(ViewModelProperty, value);
         }
 
-        object IViewFor.ViewModel
+        object? IViewFor.ViewModel
         {
             get => ViewModel;
-            set => ViewModel = (TViewModel)value;
+            set => ViewModel = (TViewModel?)value;
         }
 
-        private void OnDataContextChanged(object value)
+        private void OnDataContextChanged(object? value)
         {
             if (value is TViewModel viewModel)
             {
@@ -59,7 +59,7 @@ namespace Avalonia.ReactiveUI
             }
         }
 
-        private void OnViewModelChanged(object value)
+        private void OnViewModelChanged(object? value)
         {
             if (value == null)
             {
diff --git a/src/Avalonia.ReactiveUI/RoutedViewHost.cs b/src/Avalonia.ReactiveUI/RoutedViewHost.cs
index 421633cd58..63456bc13a 100644
--- a/src/Avalonia.ReactiveUI/RoutedViewHost.cs
+++ b/src/Avalonia.ReactiveUI/RoutedViewHost.cs
@@ -55,8 +55,8 @@ namespace Avalonia.ReactiveUI
         /// <summary>
         /// <see cref="AvaloniaProperty"/> for the <see cref="Router"/> property.
         /// </summary>
-        public static readonly StyledProperty<RoutingState> RouterProperty =
-            AvaloniaProperty.Register<RoutedViewHost, RoutingState>(nameof(Router));
+        public static readonly StyledProperty<RoutingState?> RouterProperty =
+            AvaloniaProperty.Register<RoutedViewHost, RoutingState?>(nameof(Router));
     
         /// <summary>
         /// Initializes a new instance of the <see cref="RoutedViewHost"/> class.
@@ -67,12 +67,12 @@ namespace Avalonia.ReactiveUI
             {
                 var routerRemoved = this
                     .WhenAnyValue(x => x.Router)
-                    .Where(router => router == null)
-                    .Cast<object>();
+                    .Where(router => router == null)!
+                    .Cast<object?>();
 
                 this.WhenAnyValue(x => x.Router)
                     .Where(router => router != null)
-                    .SelectMany(router => router.CurrentViewModel)
+                    .SelectMany(router => router!.CurrentViewModel)
                     .Merge(routerRemoved)
                     .Subscribe(NavigateToViewModel)
                     .DisposeWith(disposables);
@@ -82,7 +82,7 @@ namespace Avalonia.ReactiveUI
         /// <summary>
         /// Gets or sets the <see cref="RoutingState"/> of the view model stack.
         /// </summary>
-        public RoutingState Router
+        public RoutingState? Router
         {
             get => GetValue(RouterProperty);
             set => SetValue(RouterProperty, value);
@@ -91,13 +91,13 @@ namespace Avalonia.ReactiveUI
         /// <summary>
         /// Gets or sets the ReactiveUI view locator used by this router.
         /// </summary>
-        public IViewLocator ViewLocator { get; set; }
+        public IViewLocator? ViewLocator { get; set; }
     
         /// <summary>
         /// Invoked when ReactiveUI router navigates to a view model.
         /// </summary>
         /// <param name="viewModel">ViewModel to which the user navigates.</param>
-        private void NavigateToViewModel(object viewModel)
+        private void NavigateToViewModel(object? viewModel)
         {
             if (Router == null)
             {
diff --git a/src/Avalonia.ReactiveUI/TransitioningContentControl.cs b/src/Avalonia.ReactiveUI/TransitioningContentControl.cs
index cc1613ce19..9685ecbe91 100644
--- a/src/Avalonia.ReactiveUI/TransitioningContentControl.cs
+++ b/src/Avalonia.ReactiveUI/TransitioningContentControl.cs
@@ -13,20 +13,20 @@ namespace Avalonia.ReactiveUI
         /// <summary>
         /// <see cref="AvaloniaProperty"/> for the <see cref="PageTransition"/> property.
         /// </summary>
-        public static readonly StyledProperty<IPageTransition> PageTransitionProperty =
-            AvaloniaProperty.Register<TransitioningContentControl, IPageTransition>(nameof(PageTransition),
+        public static readonly StyledProperty<IPageTransition?> PageTransitionProperty =
+            AvaloniaProperty.Register<TransitioningContentControl, IPageTransition?>(nameof(PageTransition),
                 new CrossFade(TimeSpan.FromSeconds(0.5)));
 
         /// <summary>
         /// <see cref="AvaloniaProperty"/> for the <see cref="DefaultContent"/> property.
         /// </summary>
-        public static readonly StyledProperty<object> DefaultContentProperty =
-            AvaloniaProperty.Register<TransitioningContentControl, object>(nameof(DefaultContent));
+        public static readonly StyledProperty<object?> DefaultContentProperty =
+            AvaloniaProperty.Register<TransitioningContentControl, object?>(nameof(DefaultContent));
         
         /// <summary>
         /// Gets or sets the animation played when content appears and disappears.
         /// </summary>
-        public IPageTransition PageTransition
+        public IPageTransition? PageTransition
         {
             get => GetValue(PageTransitionProperty);
             set => SetValue(PageTransitionProperty, value);
@@ -35,7 +35,7 @@ namespace Avalonia.ReactiveUI
         /// <summary>
         /// Gets or sets the content displayed whenever there is no page currently routed.
         /// </summary>
-        public object DefaultContent
+        public object? DefaultContent
         {
             get => GetValue(DefaultContentProperty);
             set => SetValue(DefaultContentProperty, value);
@@ -44,7 +44,7 @@ namespace Avalonia.ReactiveUI
         /// <summary>
         /// Gets or sets the content with animation.
         /// </summary>
-        public new object Content
+        public new object? Content
         {
             get => base.Content;
             set => UpdateContentWithTransition(value);
@@ -60,7 +60,7 @@ namespace Avalonia.ReactiveUI
         /// Updates the content with transitions.
         /// </summary>
         /// <param name="content">New content to set.</param>
-        private async void UpdateContentWithTransition(object content)
+        private async void UpdateContentWithTransition(object? content)
         {
             if (PageTransition != null)
                 await PageTransition.Start(this, null, true);
diff --git a/src/Avalonia.ReactiveUI/ViewModelViewHost.cs b/src/Avalonia.ReactiveUI/ViewModelViewHost.cs
index 0169b268ca..c88323d674 100644
--- a/src/Avalonia.ReactiveUI/ViewModelViewHost.cs
+++ b/src/Avalonia.ReactiveUI/ViewModelViewHost.cs
@@ -15,8 +15,8 @@ namespace Avalonia.ReactiveUI
         /// <summary>
         /// <see cref="AvaloniaProperty"/> for the <see cref="ViewModel"/> property.
         /// </summary>
-        public static readonly AvaloniaProperty<object> ViewModelProperty =
-            AvaloniaProperty.Register<ViewModelViewHost, object>(nameof(ViewModel));
+        public static readonly AvaloniaProperty<object?> ViewModelProperty =
+            AvaloniaProperty.Register<ViewModelViewHost, object?>(nameof(ViewModel));
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ViewModelViewHost"/> class.
@@ -34,7 +34,7 @@ namespace Avalonia.ReactiveUI
         /// <summary>
         /// Gets or sets the ViewModel to display.
         /// </summary>
-        public object ViewModel
+        public object? ViewModel
         {
             get => GetValue(ViewModelProperty);
             set => SetValue(ViewModelProperty, value);
@@ -43,13 +43,13 @@ namespace Avalonia.ReactiveUI
         /// <summary>
         /// Gets or sets the view locator.
         /// </summary>
-        public IViewLocator ViewLocator { get; set; }
+        public IViewLocator? ViewLocator { get; set; }
 
         /// <summary>
         /// Invoked when ReactiveUI router navigates to a view model.
         /// </summary>
         /// <param name="viewModel">ViewModel to which the user navigates.</param>
-        private void NavigateToViewModel(object viewModel)
+        private void NavigateToViewModel(object? viewModel)
         {
             if (viewModel == null)
             {
@@ -74,4 +74,4 @@ namespace Avalonia.ReactiveUI
             Content = viewInstance;
         }
     }
-}
\ No newline at end of file
+}
diff --git a/src/Avalonia.X11/X11Window.Ime.cs b/src/Avalonia.X11/X11Window.Ime.cs
index f469ff7455..ac626f5825 100644
--- a/src/Avalonia.X11/X11Window.Ime.cs
+++ b/src/Avalonia.X11/X11Window.Ime.cs
@@ -96,14 +96,14 @@ namespace Avalonia.X11
 
         void HandleKeyEvent(ref XEvent ev)
         {
-            var index = ev.KeyEvent.state.HasFlag(XModifierMask.ShiftMask);
+            var index = ev.KeyEvent.state.HasFlagCustom(XModifierMask.ShiftMask);
 
             // We need the latin key, since it's mainly used for hotkeys, we use a different API for text anyway
             var key = (X11Key)XKeycodeToKeysym(_x11.Display, ev.KeyEvent.keycode, index ? 1 : 0).ToInt32();
                 
             // Manually switch the Shift index for the keypad,
             // there should be a proper way to do this
-            if (ev.KeyEvent.state.HasFlag(XModifierMask.Mod2Mask)
+            if (ev.KeyEvent.state.HasFlagCustom(XModifierMask.Mod2Mask)
                 && key > X11Key.Num_Lock && key <= X11Key.KP_9)
                 key = (X11Key)XKeycodeToKeysym(_x11.Display, ev.KeyEvent.keycode, index ? 0 : 1).ToInt32();
             
diff --git a/src/Avalonia.X11/X11Window.cs b/src/Avalonia.X11/X11Window.cs
index 92d1e37efe..8f3f412578 100644
--- a/src/Avalonia.X11/X11Window.cs
+++ b/src/Avalonia.X11/X11Window.cs
@@ -639,23 +639,23 @@ namespace Avalonia.X11
         RawInputModifiers TranslateModifiers(XModifierMask state)
         {
             var rv = default(RawInputModifiers);
-            if (state.HasFlag(XModifierMask.Button1Mask))
+            if (state.HasFlagCustom(XModifierMask.Button1Mask))
                 rv |= RawInputModifiers.LeftMouseButton;
-            if (state.HasFlag(XModifierMask.Button2Mask))
+            if (state.HasFlagCustom(XModifierMask.Button2Mask))
                 rv |= RawInputModifiers.RightMouseButton;
-            if (state.HasFlag(XModifierMask.Button3Mask))
+            if (state.HasFlagCustom(XModifierMask.Button3Mask))
                 rv |= RawInputModifiers.MiddleMouseButton;
-            if (state.HasFlag(XModifierMask.Button4Mask))
+            if (state.HasFlagCustom(XModifierMask.Button4Mask))
                 rv |= RawInputModifiers.XButton1MouseButton;
-            if (state.HasFlag(XModifierMask.Button5Mask))
+            if (state.HasFlagCustom(XModifierMask.Button5Mask))
                 rv |= RawInputModifiers.XButton2MouseButton;
-            if (state.HasFlag(XModifierMask.ShiftMask))
+            if (state.HasFlagCustom(XModifierMask.ShiftMask))
                 rv |= RawInputModifiers.Shift;
-            if (state.HasFlag(XModifierMask.ControlMask))
+            if (state.HasFlagCustom(XModifierMask.ControlMask))
                 rv |= RawInputModifiers.Control;
-            if (state.HasFlag(XModifierMask.Mod1Mask))
+            if (state.HasFlagCustom(XModifierMask.Mod1Mask))
                 rv |= RawInputModifiers.Alt;
-            if (state.HasFlag(XModifierMask.Mod4Mask))
+            if (state.HasFlagCustom(XModifierMask.Mod4Mask))
                 rv |= RawInputModifiers.Meta;
             return rv;
         }
diff --git a/src/Avalonia.X11/XI2Manager.cs b/src/Avalonia.X11/XI2Manager.cs
index 8cdf24cc7b..2874c517a9 100644
--- a/src/Avalonia.X11/XI2Manager.cs
+++ b/src/Avalonia.X11/XI2Manager.cs
@@ -342,13 +342,13 @@ namespace Avalonia.X11
             Type = ev->evtype;
             Timestamp = (ulong)ev->time.ToInt64();
             var state = (XModifierMask)ev->mods.Effective;
-            if (state.HasFlag(XModifierMask.ShiftMask))
+            if (state.HasFlagCustom(XModifierMask.ShiftMask))
                 Modifiers |= RawInputModifiers.Shift;
-            if (state.HasFlag(XModifierMask.ControlMask))
+            if (state.HasFlagCustom(XModifierMask.ControlMask))
                 Modifiers |= RawInputModifiers.Control;
-            if (state.HasFlag(XModifierMask.Mod1Mask))
+            if (state.HasFlagCustom(XModifierMask.Mod1Mask))
                 Modifiers |= RawInputModifiers.Alt;
-            if (state.HasFlag(XModifierMask.Mod4Mask))
+            if (state.HasFlagCustom(XModifierMask.Mod4Mask))
                 Modifiers |= RawInputModifiers.Meta;
 
             Modifiers |= ParseButtonState(ev->buttons.MaskLen, ev->buttons.Mask);
@@ -364,7 +364,7 @@ namespace Avalonia.X11
             if (Type == XiEventType.XI_ButtonPress || Type == XiEventType.XI_ButtonRelease)
                 Button = ev->detail;
             Detail = ev->detail;
-            Emulated = ev->flags.HasFlag(XiDeviceEventFlags.XIPointerEmulated);
+            Emulated = ev->flags.HasFlagCustom(XiDeviceEventFlags.XIPointerEmulated);
         }
     }
     
diff --git a/src/Linux/Avalonia.LinuxFramebuffer/LinuxFramebufferPlatform.cs b/src/Linux/Avalonia.LinuxFramebuffer/LinuxFramebufferPlatform.cs
index 340d10517d..3c8d3b5e06 100644
--- a/src/Linux/Avalonia.LinuxFramebuffer/LinuxFramebufferPlatform.cs
+++ b/src/Linux/Avalonia.LinuxFramebuffer/LinuxFramebufferPlatform.cs
@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Diagnostics;
 using System.Threading;
 using Avalonia.Controls;
@@ -79,6 +79,11 @@ namespace Avalonia.LinuxFramebuffer
                     tl.Prepare();
                     _topLevel = tl;
                     _topLevel.Renderer.Start();
+
+                    if (_topLevel is IFocusScope scope)
+                    {
+                        FocusManager.Instance?.SetFocusScope(scope);
+                    }
                 }
 
                 _topLevel.Content = value;
diff --git a/src/Linux/Avalonia.LinuxFramebuffer/Output/DrmBindings.cs b/src/Linux/Avalonia.LinuxFramebuffer/Output/DrmBindings.cs
index b5ebc4bcb7..34cc261187 100644
--- a/src/Linux/Avalonia.LinuxFramebuffer/Output/DrmBindings.cs
+++ b/src/Linux/Avalonia.LinuxFramebuffer/Output/DrmBindings.cs
@@ -54,7 +54,7 @@ namespace Avalonia.LinuxFramebuffer.Output
         }
 
         public PixelSize Resolution => new PixelSize(Mode.hdisplay, Mode.vdisplay);
-        public bool IsPreferred => Mode.type.HasFlag(DrmModeType.DRM_MODE_TYPE_PREFERRED);
+        public bool IsPreferred => Mode.type.HasFlagCustom(DrmModeType.DRM_MODE_TYPE_PREFERRED);
 
         public string Name { get; }
     }
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlIlLanguageParseIntrinsics.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlIlLanguageParseIntrinsics.cs
index 7c4cc8d28b..059b5650cb 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlIlLanguageParseIntrinsics.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlIlLanguageParseIntrinsics.cs
@@ -198,6 +198,15 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 return ConvertDefinitionList(node, text, types, types.RowDefinitions, types.RowDefinition, "row definitions", out result);
             }
 
+            if (type.Equals(types.Classes))
+            {
+                var classes = text.Split(' ');
+                var classNodes = classes.Select(c => new XamlAstTextNode(node, c, types.XamlIlTypes.String)).ToArray();
+
+                result = new AvaloniaXamlIlAvaloniaListConstantAstNode(node, types, types.Classes, types.XamlIlTypes.String, classNodes);
+                return true;
+            }
+
             result = null;
             return false;
         }
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlWellKnownTypes.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlWellKnownTypes.cs
index 125701ca9e..34aae2c5ed 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlWellKnownTypes.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlWellKnownTypes.cs
@@ -77,6 +77,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         public IXamlType RowDefinitions { get; }
         public IXamlType ColumnDefinition { get; }
         public IXamlType ColumnDefinitions { get; }
+        public IXamlType Classes { get; }
 
         public AvaloniaXamlIlWellKnownTypes(TransformerConfiguration cfg)
         {
@@ -166,6 +167,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             ColumnDefinitions = cfg.TypeSystem.GetType("Avalonia.Controls.ColumnDefinitions");
             RowDefinition = cfg.TypeSystem.GetType("Avalonia.Controls.RowDefinition");
             RowDefinitions = cfg.TypeSystem.GetType("Avalonia.Controls.RowDefinitions");
+            Classes = cfg.TypeSystem.GetType("Avalonia.Controls.Classes");
         }
     }
 
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/xamlil.github b/src/Markup/Avalonia.Markup.Xaml.Loader/xamlil.github
index ea80a607c5..f3ca2028f4 160000
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/xamlil.github
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/xamlil.github
@@ -1 +1 @@
-Subproject commit ea80a607c5e9d8f000160dbbb48c27ed4cfafbc9
+Subproject commit f3ca2028f4f64be3556a6afd22f192902de095e5
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/CompiledBindingPath.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/CompiledBindingPath.cs
index f6636664c1..11489c39aa 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/CompiledBindingPath.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/CompiledBindingPath.cs
@@ -72,7 +72,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         internal object RawSource { get; }
 
         public override string ToString()
-            => string.Concat(_elements.Select(e => e.ToString()));
+            => string.Concat(_elements);
     }
 
     public class CompiledBindingPathBuilder
@@ -88,7 +88,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
         public CompiledBindingPathBuilder Property(IPropertyInfo info, Func<WeakReference<object>, IPropertyInfo, IPropertyAccessor> accessorFactory)
         {
-            _elements.Add(new PropertyElement(info, accessorFactory));
+            _elements.Add(new PropertyElement(info, accessorFactory, _elements.Count == 0));
             return this;
         }
 
@@ -161,10 +161,13 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
     internal class PropertyElement : ICompiledBindingPathElement
     {
-        public PropertyElement(IPropertyInfo property, Func<WeakReference<object>, IPropertyInfo, IPropertyAccessor> accessorFactory)
+        private readonly bool _isFirstElement;
+
+        public PropertyElement(IPropertyInfo property, Func<WeakReference<object>, IPropertyInfo, IPropertyAccessor> accessorFactory, bool isFirstElement)
         {
             Property = property;
             AccessorFactory = accessorFactory;
+            _isFirstElement = isFirstElement;
         }
 
         public IPropertyInfo Property { get; }
@@ -172,7 +175,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         public Func<WeakReference<object>, IPropertyInfo, IPropertyAccessor> AccessorFactory { get; }
 
         public override string ToString()
-            => $".{Property.Name}";
+            => _isFirstElement ? Property.Name : $".{Property.Name}";
     }
 
     internal interface IStronglyTypedStreamElement : ICompiledBindingPathElement
diff --git a/src/Windows/Avalonia.Direct2D1/Media/Imaging/WicBitmapImpl.cs b/src/Windows/Avalonia.Direct2D1/Media/Imaging/WicBitmapImpl.cs
index 90592ea806..cac35aa4ae 100644
--- a/src/Windows/Avalonia.Direct2D1/Media/Imaging/WicBitmapImpl.cs
+++ b/src/Windows/Avalonia.Direct2D1/Media/Imaging/WicBitmapImpl.cs
@@ -42,8 +42,9 @@ namespace Avalonia.Direct2D1.Media
         public WicBitmapImpl(string fileName)
         {
             using (var decoder = new BitmapDecoder(Direct2D1Platform.ImagingFactory, fileName, DecodeOptions.CacheOnDemand))
+            using (var frame = decoder.GetFrame(0))
             {
-                WicImpl = new Bitmap(Direct2D1Platform.ImagingFactory, decoder.GetFrame(0), BitmapCreateCacheOption.CacheOnDemand);
+                WicImpl = new Bitmap(Direct2D1Platform.ImagingFactory, frame, BitmapCreateCacheOption.CacheOnDemand);
                 Dpi = new Vector(96, 96);
             }
         }
@@ -63,7 +64,8 @@ namespace Avalonia.Direct2D1.Media
             // https://stackoverflow.com/questions/48982749/decoding-image-from-stream-using-wic/48982889#48982889
             _decoder = new BitmapDecoder(Direct2D1Platform.ImagingFactory, stream, DecodeOptions.CacheOnLoad);
 
-            WicImpl = new Bitmap(Direct2D1Platform.ImagingFactory, _decoder.GetFrame(0), BitmapCreateCacheOption.CacheOnLoad);
+            using var frame = _decoder.GetFrame(0);
+            WicImpl = new Bitmap(Direct2D1Platform.ImagingFactory, frame, BitmapCreateCacheOption.CacheOnLoad);
             Dpi = new Vector(96, 96);
         }
 
@@ -120,7 +122,7 @@ namespace Avalonia.Direct2D1.Media
         {
             _decoder = new BitmapDecoder(Direct2D1Platform.ImagingFactory, stream, DecodeOptions.CacheOnLoad);
 
-            var frame = _decoder.GetFrame(0);
+            using var frame = _decoder.GetFrame(0);
 
             // now scale that to the size that we want
             var realScale = horizontal ? ((double)frame.Size.Height / frame.Size.Width) : ((double)frame.Size.Width / frame.Size.Height);
diff --git a/src/Windows/Avalonia.Win32.Interop/Wpf/WpfTopLevelImpl.cs b/src/Windows/Avalonia.Win32.Interop/Wpf/WpfTopLevelImpl.cs
index 3bb29f4e23..7d86116f38 100644
--- a/src/Windows/Avalonia.Win32.Interop/Wpf/WpfTopLevelImpl.cs
+++ b/src/Windows/Avalonia.Win32.Interop/Wpf/WpfTopLevelImpl.cs
@@ -147,13 +147,13 @@ namespace Avalonia.Win32.Interop.Wpf
         {
             var state = Keyboard.Modifiers;
             var rv = default(RawInputModifiers);
-            if (state.HasFlag(ModifierKeys.Windows))
+            if (state.HasFlagCustom(ModifierKeys.Windows))
                 rv |= RawInputModifiers.Meta;
-            if (state.HasFlag(ModifierKeys.Alt))
+            if (state.HasFlagCustom(ModifierKeys.Alt))
                 rv |= RawInputModifiers.Alt;
-            if (state.HasFlag(ModifierKeys.Control))
+            if (state.HasFlagCustom(ModifierKeys.Control))
                 rv |= RawInputModifiers.Control;
-            if (state.HasFlag(ModifierKeys.Shift))
+            if (state.HasFlagCustom(ModifierKeys.Shift))
                 rv |= RawInputModifiers.Shift;
             if (e != null)
             {
diff --git a/src/Windows/Avalonia.Win32/DataObject.cs b/src/Windows/Avalonia.Win32/DataObject.cs
index 6c1b4ef5d9..5f02796d30 100644
--- a/src/Windows/Avalonia.Win32/DataObject.cs
+++ b/src/Windows/Avalonia.Win32/DataObject.cs
@@ -181,7 +181,7 @@ namespace Avalonia.Win32
                 ole.GetData(ref format, out medium);
                 return;
             }
-            if(!format.tymed.HasFlag(TYMED.TYMED_HGLOBAL))
+            if(!format.tymed.HasFlagCustom(TYMED.TYMED_HGLOBAL))
                 Marshal.ThrowExceptionForHR(DV_E_TYMED);
 
             if (format.dwAspect != DVASPECT.DVASPECT_CONTENT)
@@ -205,7 +205,7 @@ namespace Avalonia.Win32
                 return;
             }
 
-            if (medium.tymed != TYMED.TYMED_HGLOBAL || !format.tymed.HasFlag(TYMED.TYMED_HGLOBAL))
+            if (medium.tymed != TYMED.TYMED_HGLOBAL || !format.tymed.HasFlagCustom(TYMED.TYMED_HGLOBAL))
                 Marshal.ThrowExceptionForHR(DV_E_TYMED);
 
             if (format.dwAspect != DVASPECT.DVASPECT_CONTENT)
@@ -228,7 +228,7 @@ namespace Avalonia.Win32
                 return ole.QueryGetData(ref format);
             if (format.dwAspect != DVASPECT.DVASPECT_CONTENT)
                 return DV_E_DVASPECT;
-            if (!format.tymed.HasFlag(TYMED.TYMED_HGLOBAL))
+            if (!format.tymed.HasFlagCustom(TYMED.TYMED_HGLOBAL))
                 return DV_E_TYMED;
 
             string dataFormat = ClipboardFormats.GetFormat(format.cfFormat);
diff --git a/src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs b/src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs
index 287d2c49a5..c137926e4c 100644
--- a/src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs
+++ b/src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs
@@ -1438,15 +1438,15 @@ namespace Avalonia.Win32.Interop
         }
 
         [DllImport("ntdll")]
-        private static extern int RtlGetVersion(out RTL_OSVERSIONINFOEX lpVersionInformation);
+        private static extern int RtlGetVersion(ref RTL_OSVERSIONINFOEX lpVersionInformation);
 
         internal static Version RtlGetVersion()
         {
             RTL_OSVERSIONINFOEX v = new RTL_OSVERSIONINFOEX();
             v.dwOSVersionInfoSize = (uint)Marshal.SizeOf(v);
-            if (RtlGetVersion(out v) == 0)
+            if (RtlGetVersion(ref v) == 0)
             {
-                return new Version((int)v.dwMajorVersion, (int)v.dwMinorVersion, (int)v.dwBuildNumber, (int)v.dwPlatformId);
+                return new Version((int)v.dwMajorVersion, (int)v.dwMinorVersion, (int)v.dwBuildNumber);
             }
             else
             {
diff --git a/src/Windows/Avalonia.Win32/OleDropTarget.cs b/src/Windows/Avalonia.Win32/OleDropTarget.cs
index 37d047689c..d038e341b8 100644
--- a/src/Windows/Avalonia.Win32/OleDropTarget.cs
+++ b/src/Windows/Avalonia.Win32/OleDropTarget.cs
@@ -24,11 +24,11 @@ namespace Avalonia.Win32
         public static DropEffect ConvertDropEffect(DragDropEffects operation)
         {
             DropEffect result = DropEffect.None;
-            if (operation.HasFlag(DragDropEffects.Copy))
+            if (operation.HasFlagCustom(DragDropEffects.Copy))
                 result |= DropEffect.Copy;
-            if (operation.HasFlag(DragDropEffects.Move))
+            if (operation.HasFlagCustom(DragDropEffects.Move))
                 result |= DropEffect.Move;
-            if (operation.HasFlag(DragDropEffects.Link))
+            if (operation.HasFlagCustom(DragDropEffects.Link))
                 result |= DropEffect.Link;
             return result;
         }
@@ -36,11 +36,11 @@ namespace Avalonia.Win32
         public static DragDropEffects ConvertDropEffect(DropEffect effect)
         {
             DragDropEffects result = DragDropEffects.None;
-            if (effect.HasFlag(DropEffect.Copy))
+            if (effect.HasFlagCustom(DropEffect.Copy))
                 result |= DragDropEffects.Copy;
-            if (effect.HasFlag(DropEffect.Move))
+            if (effect.HasFlagCustom(DropEffect.Move))
                 result |= DragDropEffects.Move;
-            if (effect.HasFlag(DropEffect.Link))
+            if (effect.HasFlagCustom(DropEffect.Link))
                 result |= DragDropEffects.Link;
             return result;
         }
@@ -50,17 +50,17 @@ namespace Avalonia.Win32
             var modifiers = RawInputModifiers.None;
             var state = (UnmanagedMethods.ModifierKeys)grfKeyState;
 
-            if (state.HasFlag(UnmanagedMethods.ModifierKeys.MK_LBUTTON))
+            if (state.HasFlagCustom(UnmanagedMethods.ModifierKeys.MK_LBUTTON))
                 modifiers |= RawInputModifiers.LeftMouseButton;
-            if (state.HasFlag(UnmanagedMethods.ModifierKeys.MK_MBUTTON))
+            if (state.HasFlagCustom(UnmanagedMethods.ModifierKeys.MK_MBUTTON))
                 modifiers |= RawInputModifiers.MiddleMouseButton;
-            if (state.HasFlag(UnmanagedMethods.ModifierKeys.MK_RBUTTON))
+            if (state.HasFlagCustom(UnmanagedMethods.ModifierKeys.MK_RBUTTON))
                 modifiers |= RawInputModifiers.RightMouseButton;
-            if (state.HasFlag(UnmanagedMethods.ModifierKeys.MK_SHIFT))
+            if (state.HasFlagCustom(UnmanagedMethods.ModifierKeys.MK_SHIFT))
                 modifiers |= RawInputModifiers.Shift;
-            if (state.HasFlag(UnmanagedMethods.ModifierKeys.MK_CONTROL))
+            if (state.HasFlagCustom(UnmanagedMethods.ModifierKeys.MK_CONTROL))
                 modifiers |= RawInputModifiers.Control;
-            if (state.HasFlag(UnmanagedMethods.ModifierKeys.MK_ALT))
+            if (state.HasFlagCustom(UnmanagedMethods.ModifierKeys.MK_ALT))
                 modifiers |= RawInputModifiers.Alt;
             return modifiers;
         }
diff --git a/src/Windows/Avalonia.Win32/WindowImpl.CustomCaptionProc.cs b/src/Windows/Avalonia.Win32/WindowImpl.CustomCaptionProc.cs
index 68bd40da79..0a8648aa9a 100644
--- a/src/Windows/Avalonia.Win32/WindowImpl.CustomCaptionProc.cs
+++ b/src/Windows/Avalonia.Win32/WindowImpl.CustomCaptionProc.cs
@@ -23,13 +23,13 @@ namespace Avalonia.Win32
             AdjustWindowRectEx(ref rcFrame, (uint)(WindowStyles.WS_OVERLAPPEDWINDOW & ~WindowStyles.WS_CAPTION), false, 0);
 
             var borderThickness = new RECT();
-            if (GetStyle().HasFlag(WindowStyles.WS_THICKFRAME))
+            if (GetStyle().HasFlagCustom(WindowStyles.WS_THICKFRAME))
             {
                 AdjustWindowRectEx(ref borderThickness, (uint)(GetStyle()), false, 0);
                 borderThickness.left *= -1;
                 borderThickness.top *= -1;
             }
-            else if (GetStyle().HasFlag(WindowStyles.WS_BORDER))
+            else if (GetStyle().HasFlagCustom(WindowStyles.WS_BORDER))
             {
                 borderThickness = new RECT { bottom = 1, left = 1, right = 1, top = 1 };
             }
diff --git a/src/Windows/Avalonia.Win32/WindowImpl.cs b/src/Windows/Avalonia.Win32/WindowImpl.cs
index 5e67c0d7f3..2f980cfe86 100644
--- a/src/Windows/Avalonia.Win32/WindowImpl.cs
+++ b/src/Windows/Avalonia.Win32/WindowImpl.cs
@@ -836,7 +836,7 @@ namespace Avalonia.Win32
             borderCaptionThickness.left *= -1;
             borderCaptionThickness.top *= -1;
 
-            bool wantsTitleBar = _extendChromeHints.HasFlag(ExtendClientAreaChromeHints.SystemChrome) || _extendTitleBarHint == -1;
+            bool wantsTitleBar = _extendChromeHints.HasFlagCustom(ExtendClientAreaChromeHints.SystemChrome) || _extendTitleBarHint == -1;
 
             if (!wantsTitleBar)
             {
@@ -853,7 +853,7 @@ namespace Avalonia.Win32
                 borderCaptionThickness.top = (int)(_extendTitleBarHint * RenderScaling);                
             }
 
-            margins.cyTopHeight = _extendChromeHints.HasFlag(ExtendClientAreaChromeHints.SystemChrome) && !_extendChromeHints.HasFlag(ExtendClientAreaChromeHints.PreferSystemChrome) ? borderCaptionThickness.top : 1;
+            margins.cyTopHeight = _extendChromeHints.HasFlagCustom(ExtendClientAreaChromeHints.SystemChrome) && !_extendChromeHints.HasFlagCustom(ExtendClientAreaChromeHints.PreferSystemChrome) ? borderCaptionThickness.top : 1;
 
             if (WindowState == WindowState.Maximized)
             {
@@ -901,8 +901,8 @@ namespace Avalonia.Win32
                 _extendedMargins = new Thickness();
             }
 
-            if(!_isClientAreaExtended || (_extendChromeHints.HasFlag(ExtendClientAreaChromeHints.SystemChrome) &&
-                !_extendChromeHints.HasFlag(ExtendClientAreaChromeHints.PreferSystemChrome)))
+            if(!_isClientAreaExtended || (_extendChromeHints.HasFlagCustom(ExtendClientAreaChromeHints.SystemChrome) &&
+                !_extendChromeHints.HasFlagCustom(ExtendClientAreaChromeHints.PreferSystemChrome)))
             {
                 EnableCloseButton(_hwnd);
             }
@@ -1239,7 +1239,7 @@ namespace Avalonia.Win32
         public Action<bool> ExtendClientAreaToDecorationsChanged { get; set; }
         
         /// <inheritdoc/>
-        public bool NeedsManagedDecorations => _isClientAreaExtended && _extendChromeHints.HasFlag(ExtendClientAreaChromeHints.PreferSystemChrome);
+        public bool NeedsManagedDecorations => _isClientAreaExtended && _extendChromeHints.HasFlagCustom(ExtendClientAreaChromeHints.PreferSystemChrome);
 
         /// <inheritdoc/>
         public Thickness ExtendedMargins => _extendedMargins;
diff --git a/tests/Avalonia.Input.UnitTests/InputElement_Focus.cs b/tests/Avalonia.Input.UnitTests/InputElement_Focus.cs
index 8b8f2fa775..602455ba36 100644
--- a/tests/Avalonia.Input.UnitTests/InputElement_Focus.cs
+++ b/tests/Avalonia.Input.UnitTests/InputElement_Focus.cs
@@ -318,5 +318,24 @@ namespace Avalonia.Input.UnitTests
                 Assert.True(root2.IsKeyboardFocusWithin);
             }
         }
+
+        [Fact]
+        public void Can_Clear_Focus()
+        {
+            Button target;
+
+            using (UnitTestApplication.Start(TestServices.RealFocus))
+            {
+                var root = new TestRoot
+                {
+                    Child = target = new Button()
+                };
+
+                target.Focus();
+                FocusManager.Instance.Focus(null);
+
+                Assert.Null(FocusManager.Instance.Current);
+            }
+        }
     }
 }