Add WPF MC3063 breaking change documentation for empty Grid definitions

Co-authored-by: gewarren <[email protected]>

Author: Copilot

docs/core/compatibility/10.0.md

@@ -118,4 +118,5 @@ If you're migrating an app to .NET 10, the breaking changes listed here might af
 
 | Title | Type of change                        | Introduced version |
 |-------|---------------------------------------|--------------------|
+| [WPF throws MC3063 error for empty ColumnDefinitions or RowDefinitions](wpf/10.0/empty-grid-definitions.md) | Source incompatible | Preview 5          |
 | [Incorrect usage of DynamicResource causes application crash](wpf/10.0/dynamicresource-crash.md) | Source incompatible/behavioral change | Preview 4          |

docs/core/compatibility/toc.yml

@@ -130,6 +130,8 @@ items:
                 href: windows-forms/10.0/statusstrip-renderer.md
           - name: WPF
             items:
+              - name: WPF throws MC3063 error for empty ColumnDefinitions or RowDefinitions
+                href: wpf/10.0/empty-grid-definitions.md
               - name: Incorrect usage of DynamicResource causes application crash
                 href: wpf/10.0/dynamicresource-crash.md
       - name: .NET 9

docs/core/compatibility/wpf/10.0/empty-grid-definitions.md

@@ -0,0 +1,84 @@
+---
+title: "Breaking change - WPF throws MC3063 error for empty ColumnDefinitions or RowDefinitions"
+description: "Learn about the breaking change in .NET 10 where empty Grid.ColumnDefinitions or Grid.RowDefinitions declarations now cause MC3063 compilation errors."
+ms.date: 01/27/2025
+ai-usage: ai-assisted
+ms.custom: https://github.com/dotnet/docs/issues/47743
+---
+
+# WPF throws MC3063 error for empty ColumnDefinitions or RowDefinitions
+
+Starting with .NET 10 Preview 5, WPF applications fail to build if `<Grid.ColumnDefinitions>` or `<Grid.RowDefinitions>` are declared but left empty in XAML. This results in error **MC3063**, indicating that the property doesn't have a value.
+
+## Version introduced
+
+.NET 10 Preview 5
+
+## Previous behavior
+
+WPF applications with empty `<Grid.ColumnDefinitions>` or `<Grid.RowDefinitions>` compiled successfully, even though the layout definitions were incomplete. WPF would default to a single row and column, placing all child elements in that single cell unless otherwise specified.
+
+Example that previously compiled:
+
+```xml
+<Grid>
+  <Grid.ColumnDefinitions>
+  </Grid.ColumnDefinitions>
+  <Grid.RowDefinitions>
+  </Grid.RowDefinitions>
+  <TextBlock Text="Hello World" />
+</Grid>
+```
+
+## New behavior
+
+The same code now fails to compile with the following error:
+
+```output
+error MC3063: Property 'ColumnDefinitions' does not have a value.
+error MC3063: Property 'RowDefinitions' does not have a value.
+```
+
+This occurs when `<Grid.ColumnDefinitions>` or `<Grid.RowDefinitions>` elements are declared but contain no child `<ColumnDefinition />` or `<RowDefinition />` elements.
+
+## Type of breaking change
+
+This is a [source-incompatible](../../categories.md#source-compatibility) change.
+
+## Reason for change
+
+This change is a direct consequence of implementing Grid XAML Shorthand Syntax support. The enhancement improves XAML parsing by being more strict about property declarations that don't contain meaningful content.
+
+## Recommended action
+
+Choose one of the following approaches to resolve the compilation error:
+
+### Option 1: Remove empty declarations
+
+Remove the empty `<Grid.ColumnDefinitions>` and `<Grid.RowDefinitions>` elements entirely:
+
+```xml
+<Grid>
+  <TextBlock Text="Hello World" />
+</Grid>
+```
+
+### Option 2: Add actual definitions
+
+If you need specific column or row definitions, add the appropriate `<ColumnDefinition />` or `<RowDefinition />` elements:
+
+```xml
+<Grid>
+  <Grid.ColumnDefinitions>
+    <ColumnDefinition />
+  </Grid.ColumnDefinitions>
+  <Grid.RowDefinitions>
+    <RowDefinition />
+  </Grid.RowDefinitions>
+  <TextBlock Text="Hello World" />
+</Grid>
+```
+
+## Affected APIs
+
+None.