Add breaking change documentation for DefaultValueAttribute DynamicallyAccessedMembers removal

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

Author: Copilot

docs/core/compatibility/10.0.md

@@ -39,6 +39,7 @@ If you're migrating an app to .NET 10, the breaking changes listed here might af
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 | [Consistent shift behavior in generic math](core-libraries/10.0/generic-math.md) | Behavioral change | Preview 1 |
+| [DefaultValueAttribute(System.Type type, string? value) constructor no longer annotated with DynamicallyAccessedMembers](core-libraries/10.0/defaultvalueattribute-dynamically-accessed-members.md) | Binary incompatible/source incompatible | Preview 1 |
 | [Default trace context propagator updated to W3C standard](core-libraries/10.0/default-trace-context-propagator.md) | Behavioral change | Preview 4 |
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docs/core/compatibility/core-libraries/10.0/defaultvalueattribute-dynamically-accessed-members.md

@@ -0,0 +1,38 @@
+---
+title: "Breaking change: DefaultValueAttribute(System.Type type, string? value) constructor no longer annotated with DynamicallyAccessedMembers"
+description: "Learn about the breaking change in .NET 10 where DefaultValueAttribute(System.Type type, string? value) constructor is no longer annotated with DynamicallyAccessedMembers."
+ms.date: 01/30/2025
+ai-usage: ai-assisted
+---
+
+# DefaultValueAttribute(System.Type type, string? value) constructor no longer annotated with DynamicallyAccessedMembers
+
+The <xref:System.ComponentModel.DefaultValueAttribute.%23ctor(System.Type,System.String)?displayProperty=nameWithType> constructor is no longer annotated with <xref:System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute>. This constructor is not supported with trimming and will throw an exception if reached at runtime in a trimmed app.
+
+## Version introduced
+
+.NET 10
+
+## Previous behavior
+
+If the constructor was used in a trimmed app and the feature switch to disable exception throwing was used, publishing the app would generate a trimming warning and there was a chance the code would work at runtime.
+
+## New behavior
+
+If the constructor is used in a trimmed app and the feature switch to disable exception throwing is used, publishing the app will generate a trimming warning and there's a smaller chance the code will work at runtime.
+
+## Type of breaking change
+
+This change can affect [binary compatibility](../../categories.md#binary-compatibility) and [source compatibility](../../categories.md#source-compatibility).
+
+## Reason for change
+
+This attribute should not be used in trimmed apps because it doesn't reliably work. Trimming should be free to remove type members mentioned in the attribute.
+
+## Recommended action
+
+Do not enable the feature switch that attempts to make this attribute (unreliably) work in trimmed apps.
+
+## Affected APIs
+
+- <xref:System.ComponentModel.DefaultValueAttribute.%23ctor(System.Type,System.String)?displayProperty=fullName>