Added docs to clarify difference with SizeChanged.

src/Avalonia.Controls/WindowBase.cs

@@ -83,6 +83,19 @@ namespace Avalonia.Controls
         /// <summary>
         /// Occurs when the window is resized.
         /// </summary>
+        /// <remarks>
+        /// Although this event is similar to the <see cref="Control.SizeChanged"/> event, they are
+        /// conceptually different:
+        /// 
+        /// - <see cref="Resized"/> is a window-level event, fired when a resize notification arrives
+        ///   from the platform windowing subsystem. The event args contain details of the source of
+        ///   the resize event in the <see cref="WindowResizedEventArgs.Reason"/> property. This
+        ///   event is raised before layout has been run on the window's content.
+        /// - <see cref="Control.SizeChanged"/> is a layout-level event, fired when a layout pass
+        ///   completes on a control. <see cref="Control.SizeChanged"/> is present on all controls
+        ///   and is fired when the control's size changes for any reason, including a
+        ///   <see cref="Resized"/> event in the case of a Window.
+        /// </remarks>
         public event EventHandler<WindowResizedEventArgs>? Resized;
 
         public new IWindowBaseImpl? PlatformImpl => (IWindowBaseImpl?) base.PlatformImpl;