Added AccessibilityView and ControlType.

- `AutomationProperties.AccessibilityView`: from UWP - control's element's visibility in automation tree
- `ControlTypeOverride`: from UWP proposal - overrides the automation control type specified in peer

src/Avalonia.Controls/Automation/AutomationProperties.cs

@@ -1,8 +1,30 @@
 using System;
+using Avalonia.Automation.Peers;
 using Avalonia.Controls;
 
 namespace Avalonia.Automation
 {
+    /// <summary>
+    /// Declares how a control should included in different views of the automation tree.
+    /// </summary>
+    public enum AccessibilityView
+    {
+        /// <summary>
+        /// The control is included in the Raw view of the automation tree.
+        /// </summary>
+        Raw,
+
+        /// <summary>
+        /// The control is included in the Control view of the automation tree.
+        /// </summary>
+        Control,
+
+        /// <summary>
+        /// The control is included in the Content view of the automation tree.
+        /// </summary>
+        Content,
+    }
+
     public static class AutomationProperties
     {
         internal const int AutomationPositionInSetDefault = -1;
@@ -16,6 +38,15 @@ namespace Avalonia.Automation
                 "AcceleratorKey",
                 typeof(AutomationProperties));
 
+        /// <summary>
+        /// Defines the AutomationProperties.AccessibilityView attached property.
+        /// </summary>
+        public static readonly AttachedProperty<AccessibilityView> AccessibilityViewProperty =
+            AvaloniaProperty.RegisterAttached<StyledElement, AccessibilityView>(
+                "AccessibilityView",
+                typeof(AutomationProperties),
+                defaultValue: AccessibilityView.Content);
+
         /// <summary>
         /// Defines the AutomationProperties.AccessKey attached property
         /// </summary>
@@ -32,6 +63,14 @@ namespace Avalonia.Automation
                 "AutomationId",
                 typeof(AutomationProperties));
 
+        /// <summary>
+        /// Defines the AutomationProperties.ControlTypeOverride attached property.
+        /// </summary>
+        public static readonly AttachedProperty<AutomationControlType?> ControlTypeOverrideProperty =
+            AvaloniaProperty.RegisterAttached<StyledElement, AutomationControlType?>(
+                "ControlTypeOverride",
+                typeof(AutomationProperties));
+
         /// <summary>
         /// Defines the AutomationProperties.HelpText attached property.
         /// </summary>
@@ -171,6 +210,32 @@ namespace Avalonia.Automation
             return ((string)element.GetValue(AcceleratorKeyProperty));
         }
 
+        /// <summary>
+        /// Helper for setting AccessibilityView property on a StyledElement. 
+        /// </summary>
+        public static void SetAccessibilityView(StyledElement element, AccessibilityView value)
+        {
+            if (element == null)
+            {
+                throw new ArgumentNullException(nameof(element));
+            }
+
+            element.SetValue(AccessibilityViewProperty, value);
+        }
+
+        /// <summary>
+        /// Helper for reading AccessibilityView property from a StyledElement.
+        /// </summary>
+        public static AccessibilityView GetAccessibilityView(StyledElement element)
+        {
+            if (element == null)
+            {
+                throw new ArgumentNullException(nameof(element));
+            }
+
+            return element.GetValue(AccessibilityViewProperty);
+        }
+
         /// <summary>
         /// Helper for setting AccessKey property on a StyledElement. 
         /// </summary>
@@ -223,6 +288,32 @@ namespace Avalonia.Automation
             return element.GetValue(AutomationIdProperty);
         }
 
+        /// <summary>
+        /// Helper for setting ControlTypeOverride property on a StyledElement. 
+        /// </summary>
+        public static void SetControlTypeOverride(StyledElement element, AutomationControlType? value)
+        {
+            if (element == null)
+            {
+                throw new ArgumentNullException(nameof(element));
+            }
+
+            element.SetValue(ControlTypeOverrideProperty, value);
+        }
+
+        /// <summary>
+        /// Helper for reading ControlTypeOverride property from a StyledElement.
+        /// </summary>
+        public static AutomationControlType? GetControlTypeOverride(StyledElement element)
+        {
+            if (element == null)
+            {
+                throw new ArgumentNullException(nameof(element));
+            }
+
+            return element.GetValue(ControlTypeOverrideProperty);
+        }
+
         /// <summary>
         /// Helper for setting HelpText property on a StyledElement. 
         /// </summary>

src/Avalonia.Controls/Automation/Peers/AutomationPeer.cs

@@ -74,7 +74,7 @@ namespace Avalonia.Automation.Peers
         /// <summary>
         /// Gets the control type for the element that is associated with the UI Automation peer.
         /// </summary>
-        public AutomationControlType GetAutomationControlType() => GetAutomationControlTypeCore();
+        public AutomationControlType GetAutomationControlType() => GetControlTypeOverrideCore();
 
         /// <summary>
         /// Gets the automation ID of the element that is associated with the UI Automation peer.
@@ -230,7 +230,12 @@ namespace Avalonia.Automation.Peers
         protected abstract bool IsKeyboardFocusableCore();
         protected abstract void SetFocusCore();
         protected abstract bool ShowContextMenuCore();
-        
+
+        protected virtual AutomationControlType GetControlTypeOverrideCore()
+        {
+            return GetAutomationControlTypeCore();
+        }
+
         protected virtual object? GetProviderCore(Type providerType)
         {
             return providerType.IsAssignableFrom(this.GetType()) ? this : null;

src/Avalonia.Controls/Automation/Peers/ControlAutomationPeer.cs

@@ -148,17 +148,22 @@ namespace Avalonia.Automation.Peers
 
         protected override string? GetAcceleratorKeyCore() => AutomationProperties.GetAcceleratorKey(Owner);
         protected override string? GetAccessKeyCore() => AutomationProperties.GetAccessKey(Owner);
+        protected override AutomationControlType GetAutomationControlTypeCore() => AutomationControlType.Custom;
         protected override string? GetAutomationIdCore() => AutomationProperties.GetAutomationId(Owner) ?? Owner.Name;
         protected override Rect GetBoundingRectangleCore() => GetBounds(Owner.TransformedBounds);
-        protected override AutomationControlType GetAutomationControlTypeCore() => AutomationControlType.Custom;
         protected override string GetClassNameCore() => Owner.GetType().Name;
         protected override bool HasKeyboardFocusCore() => Owner.IsFocused;
-        protected override bool IsContentElementCore() => true;
-        protected override bool IsControlElementCore() => true;
+        protected override bool IsContentElementCore() => AutomationProperties.GetAccessibilityView(Owner) >= AccessibilityView.Content;
+        protected override bool IsControlElementCore() => AutomationProperties.GetAccessibilityView(Owner) >= AccessibilityView.Control;
         protected override bool IsEnabledCore() => Owner.IsEnabled;
         protected override bool IsKeyboardFocusableCore() => Owner.Focusable;
         protected override void SetFocusCore() => Owner.Focus();
 
+        protected override AutomationControlType GetControlTypeOverrideCore()
+        {
+            return AutomationProperties.GetControlTypeOverride(Owner) ?? GetAutomationControlTypeCore();
+        }
+
         private static Rect GetBounds(TransformedBounds? bounds)
         {
             return bounds?.Bounds.TransformToAABB(bounds!.Value.Transform) ?? default;