From 1e578c1a48bf8d72470dca0f1bb9c35bbabe3d17 Mon Sep 17 00:00:00 2001
From: Petr Onderka <petronderka@microsoft.com>
Date: Tue, 7 Jul 2026 02:11:45 +0200
Subject: [PATCH 1/5] Remove outdated labels from breaking change issue
 template (#54637)

Removed 'Pri1' and 'doc-idea' labels from breaking change issue template. These labels don't seem to exist anymore.
---
 .github/ISSUE_TEMPLATE/02-breaking-change.yml | 2 --
 1 file changed, 2 deletions(-)

diff --git a/.github/ISSUE_TEMPLATE/02-breaking-change.yml b/.github/ISSUE_TEMPLATE/02-breaking-change.yml
index c837773a91214..02362a5760b58 100644
--- a/.github/ISSUE_TEMPLATE/02-breaking-change.yml
+++ b/.github/ISSUE_TEMPLATE/02-breaking-change.yml
@@ -3,8 +3,6 @@ description: This template is for .NET product team members to report breaking c
 title: "[Breaking change]: "
 labels:
   - breaking-change
-  - Pri1
-  - doc-idea
 assignees:
  - gewarren
 body:

From 1c025e21075e974af11ae50184ea0a3bc00c4551 Mon Sep 17 00:00:00 2001
From: Copilot <198982749+Copilot@users.noreply.github.com>
Date: Tue, 7 Jul 2026 07:50:47 -0700
Subject: [PATCH 2/5] Document breaking change: AsnEncodedData.RawData setter
 obsoleted (SYSLIB0065) in .NET 11 (#54644)

* Initial plan

* Add breaking change doc for AsnEncodedData.RawData setter obsolete (SYSLIB0065)

* Consolidate AsnEncodedData SYSLIB0065 into obsolete-apis.md per reviewer feedback

* Update docs/core/compatibility/core-libraries/11/obsolete-apis.md

* Move SYSLIB0065 obsoletion to cryptography page

* Fix core .NET capitalization in cryptography obsoletion page

* Rewrite cryptography obsoletion guidance as prose

* Align obsoletion pages with docs style

* Update obsolete-apis.md

* Update docs/core/compatibility/core-libraries/11/obsolete-apis.md

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Genevieve Warren <24882762+gewarren@users.noreply.github.com>
---
 docs/core/compatibility/11.md                 |  1 +
 .../core-libraries/11/obsolete-apis.md        |  6 +-
 .../cryptography/11/obsolete-apis.md          | 49 +++++++++++++
 docs/core/compatibility/toc.yml               |  2 +
 .../obsoletions-overview.md                   |  1 +
 .../syslib-diagnostics/syslib0065.md          | 73 +++++++++++++++++++
 docs/navigate/tools-diagnostics/toc.yml       |  2 +
 7 files changed, 132 insertions(+), 2 deletions(-)
 create mode 100644 docs/core/compatibility/cryptography/11/obsolete-apis.md
 create mode 100644 docs/fundamentals/syslib-diagnostics/syslib0065.md

diff --git a/docs/core/compatibility/11.md b/docs/core/compatibility/11.md
index 7d83696490c96..554f327f2b3d5 100644
--- a/docs/core/compatibility/11.md
+++ b/docs/core/compatibility/11.md
@@ -39,6 +39,7 @@ See [Breaking changes in ASP.NET Core 11](/aspnet/core/breaking-changes/11/overv
 
 | Title                                                          | Type of change    |
 |----------------------------------------------------------------|-------------------|
+| [API obsoletions](cryptography/11/obsolete-apis.md)            | Source incompatible |
 | [DSA removed from macOS](cryptography/11/dsa-removed-macos.md) | Behavioral change |
 
 <!--
diff --git a/docs/core/compatibility/core-libraries/11/obsolete-apis.md b/docs/core/compatibility/core-libraries/11/obsolete-apis.md
index 7e07c35c74f30..1b4fac7881b49 100644
--- a/docs/core/compatibility/core-libraries/11/obsolete-apis.md
+++ b/docs/core/compatibility/core-libraries/11/obsolete-apis.md
@@ -2,11 +2,12 @@
 title: "Breaking change: .NET 11 obsoletions with custom IDs"
 titleSuffix: ""
 description: Learn about the APIs that have been marked as obsolete in .NET 11 with a custom diagnostic ID.
-ms.date: 04/03/2026
+ms.date: 07/06/2026
+ai-usage: ai-assisted
 ---
 # API obsoletions with non-default diagnostic IDs (.NET 11)
 
-Some APIs have been marked as obsolete, starting in .NET 11.
+Some APIs are marked as obsolete, starting in .NET 11.
 
 This breaking change is specific to APIs that have been marked as obsolete *with a custom diagnostic ID*. Suppressing the default obsoletion diagnostic ID, which is [CS0618](../../../../csharp/language-reference/compiler-messages/cs0618.md) for the C# compiler, does not suppress the warnings that the compiler generates when these APIs are used.
 
@@ -43,6 +44,7 @@ These obsoletions can affect [source compatibility](../../categories.md#source-c
 
 ## See also
 
+- [Cryptography obsoletions (.NET 11)](../../cryptography/11/obsolete-apis.md)
 - [API obsoletions with non-default diagnostic IDs (.NET 10)](../10.0/obsolete-apis.md)
 - [API obsoletions with non-default diagnostic IDs (.NET 9)](../9.0/obsolete-apis-with-custom-diagnostics.md)
 - [API obsoletions with non-default diagnostic IDs (.NET 8)](../8.0/obsolete-apis-with-custom-diagnostics.md)
diff --git a/docs/core/compatibility/cryptography/11/obsolete-apis.md b/docs/core/compatibility/cryptography/11/obsolete-apis.md
new file mode 100644
index 0000000000000..9fa8c69a5cbcc
--- /dev/null
+++ b/docs/core/compatibility/cryptography/11/obsolete-apis.md
@@ -0,0 +1,49 @@
+---
+title: "Breaking change: .NET 11 obsoletions in cryptography"
+titleSuffix: ""
+description: Learn about the cryptography APIs that have been marked as obsolete in .NET 11.
+ms.date: 07/06/2026
+ai-usage: ai-assisted
+---
+# Cryptography obsoletions (.NET 11)
+
+Some cryptography APIs are marked as obsolete, starting in .NET 11.
+
+For obsoletions in other core .NET library areas, see [API obsoletions with non-default diagnostic IDs (.NET 11)](../../core-libraries/11/obsolete-apis.md).
+
+## Previous behavior
+
+Previously, you could use these APIs without any compile-time warnings about obsoletion.
+
+## New behavior
+
+In .NET 11 and later versions, using these APIs produces a compile-time diagnostic.
+
+The following table lists the custom diagnostic IDs and their corresponding warning messages.
+
+| Diagnostic ID | Description | Severity |
+|---------------|-------------|----------|
+| [SYSLIB0065](../../../../fundamentals/syslib-diagnostics/syslib0065.md) | The `set` accessor of <xref:System.Security.Cryptography.AsnEncodedData.RawData?displayProperty=nameWithType> is obsolete. Use the constructor of the appropriate type to decode data, or use <xref:System.Security.Cryptography.AsnEncodedData.CopyFrom(System.Security.Cryptography.AsnEncodedData)?displayProperty=nameWithType> for mutable scenarios. | Warning |
+
+## Version introduced
+
+.NET 11 Preview 6
+
+## Type of breaking change
+
+These obsoletions can affect [source compatibility](../../categories.md#source-compatibility).
+
+## Recommended action
+
+If you must keep use the obsolete APIs, suppress the warning by using the custom diagnostic ID.
+
+## Affected APIs
+
+### SYSLIB0065
+
+- `set` accessor of <xref:System.Security.Cryptography.AsnEncodedData.RawData?displayProperty=fullName>
+
+## See also
+
+- [SYSLIB0065: AsnEncodedData.RawData setter is obsolete](../../../../fundamentals/syslib-diagnostics/syslib0065.md)
+- [API obsoletions with non-default diagnostic IDs (.NET 11)](../../core-libraries/11/obsolete-apis.md)
diff --git a/docs/core/compatibility/toc.yml b/docs/core/compatibility/toc.yml
index 1395fa691738d..88869b0c91be1 100644
--- a/docs/core/compatibility/toc.yml
+++ b/docs/core/compatibility/toc.yml
@@ -36,6 +36,8 @@ items:
                 href: core-libraries/11/ziparchive-createasync-eager-load.md
           - name: Cryptography
             items:
+              - name: API obsoletions
+                href: cryptography/11/obsolete-apis.md
               - name: DSA removed from macOS
                 href: cryptography/11/dsa-removed-macos.md
           - name: Extensions
diff --git a/docs/fundamentals/syslib-diagnostics/obsoletions-overview.md b/docs/fundamentals/syslib-diagnostics/obsoletions-overview.md
index b759faaeb706f..7497bacaee2e6 100644
--- a/docs/fundamentals/syslib-diagnostics/obsoletions-overview.md
+++ b/docs/fundamentals/syslib-diagnostics/obsoletions-overview.md
@@ -88,6 +88,7 @@ The following table lists the `SYSLIB0XXX` obsoletions in .NET 5+.
 | [SYSLIB0061](syslib0061.md) | Warning | The `Queryable` <xref:System.Linq.Queryable.MaxBy``2(System.Linq.IQueryable{``0},System.Linq.Expressions.Expression{System.Func{``0,``1}},System.Collections.Generic.IComparer{``0})?displayProperty=nameWithType> and <xref:System.Linq.Queryable.MinBy``2(System.Linq.IQueryable{``0},System.Linq.Expressions.Expression{System.Func{``0,``1}},System.Collections.Generic.IComparer{``0})?displayProperty=nameWithType> taking an `IComparer<TSource>` are obsolete. Use the new ones that take an `IComparer<TKey>`. |
 | [SYSLIB0062](syslib0062.md) | Warning | <xref:System.Xml.Xsl.XsltSettings.EnableScript?displayProperty=nameWithType> is obsolete. |
 | [SYSLIB0064](syslib0064.md) | Warning | <xref:System.Security.Cryptography.RSACryptoServiceProvider.Encrypt(System.Byte[],System.Boolean)?displayProperty=nameWithType> and <xref:System.Security.Cryptography.RSACryptoServiceProvider.Decrypt(System.Byte[],System.Boolean)?displayProperty=nameWithType> are obsolete. Use the overloads that accept an <xref:System.Security.Cryptography.RSAEncryptionPadding> instead. |
+| [SYSLIB0065](syslib0065.md) | Warning | The `set` accessor of <xref:System.Security.Cryptography.AsnEncodedData.RawData?displayProperty=nameWithType> is obsolete. Use the constructor of the appropriate type to decode data, or use <xref:System.Security.Cryptography.AsnEncodedData.CopyFrom(System.Security.Cryptography.AsnEncodedData)?displayProperty=nameWithType> for mutable scenarios. |
 
 ## EXTOBS obsoletions
 
diff --git a/docs/fundamentals/syslib-diagnostics/syslib0065.md b/docs/fundamentals/syslib-diagnostics/syslib0065.md
new file mode 100644
index 0000000000000..45c35bc0aa787
--- /dev/null
+++ b/docs/fundamentals/syslib-diagnostics/syslib0065.md
@@ -0,0 +1,73 @@
+---
+title: SYSLIB0065 warning - AsnEncodedData.RawData setter is obsolete
+description: Learn about the obsoletion of the AsnEncodedData.RawData property setter. Use of this setter generates compile-time warning SYSLIB0065.
+ms.date: 07/05/2026
+ai-usage: ai-assisted
+f1_keywords:
+  - SYSLIB0065
+---
+
+# SYSLIB0065: AsnEncodedData.RawData setter is obsolete
+
+Starting in .NET 11, the `set` accessor of <xref:System.Security.Cryptography.AsnEncodedData.RawData?displayProperty=nameWithType> is obsolete. Setting this property in code generates warning `SYSLIB0065` at compile time.
+
+## Reason for obsoletion
+
+<xref:System.Security.Cryptography.AsnEncodedData> represents an ASN.1-encoded object. Many types derive from it, such as <xref:System.Security.Cryptography.X509Certificates.X509BasicConstraintsExtension>, and cache their decoded representation so that property access doesn't repeatedly decode the ASN.1.
+
+Because `RawData` is not `virtual`, setting it on a derived instance causes a discrepancy between the cached decoded state and the new raw data. The derived type can't detect that the raw data changed, so it continues to return stale decoded values. For example:
+
+```csharp
+X509BasicConstraintsExtension extension = new(
+    certificateAuthority: true,
+    hasPathLengthConstraint: true,
+    pathLengthConstraint: 3,
+    critical: true);
+
+X509BasicConstraintsExtension decoded = new();
+decoded.RawData = extension.RawData;
+Console.WriteLine(decoded.CertificateAuthority);      // Unexpectedly prints False
+Console.WriteLine(decoded.HasPathLengthConstraint);   // Unexpectedly prints False
+Console.WriteLine(decoded.PathLengthConstraint);      // Unexpectedly prints 0
+```
+
+## Workaround
+
+To maintain coherency between the decoded state and the underlying data, use the constructor of the appropriate type to decode data. Treat instances as read-only—construct a new instance instead of reusing an existing one.
+
+```csharp
+// Instead of setting RawData, use the constructor.
+X509BasicConstraintsExtension decoded = new(extension, extension.Critical);
+```
+
+If you need mutable behavior, use <xref:System.Security.Cryptography.AsnEncodedData.CopyFrom(System.Security.Cryptography.AsnEncodedData)?displayProperty=nameWithType>. The `CopyFrom` method is `virtual`, so derived types can invalidate their decoded state when the raw data changes.
+
+## Suppress a warning
+
+If you must use the obsolete setter, you can suppress the warning in code or in your project file.
+
+To suppress only a single violation, add preprocessor directives to your source file to disable and then re-enable the warning.
+
+```csharp
+// Disable the warning.
+#pragma warning disable SYSLIB0065
+
+// Code that uses obsolete API.
+// ...
+
+// Re-enable the warning.
+#pragma warning restore SYSLIB0065
+```
+
+To suppress all `SYSLIB0065` warnings in your project, add a `<NoWarn>` property to your project file.
+
+```xml
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+   ...
+   <NoWarn>$(NoWarn);SYSLIB0065</NoWarn>
+  </PropertyGroup>
+</Project>
+```
+
+For more information, see [Suppress warnings](obsoletions-overview.md#suppress-warnings).
diff --git a/docs/navigate/tools-diagnostics/toc.yml b/docs/navigate/tools-diagnostics/toc.yml
index 06f6442817523..d5ceb222cd3a3 100644
--- a/docs/navigate/tools-diagnostics/toc.yml
+++ b/docs/navigate/tools-diagnostics/toc.yml
@@ -4093,6 +4093,8 @@ items:
             href: ../../fundamentals/syslib-diagnostics/syslib0062.md
           - name: SYSLIB0064
             href: ../../fundamentals/syslib-diagnostics/syslib0064.md
+          - name: SYSLIB0065
+            href: ../../fundamentals/syslib-diagnostics/syslib0065.md
       - name: Experimental features
         items:
           - name: Overview

From 776996387ef266506f7aa4ee3d73dd09cae8f45a Mon Sep 17 00:00:00 2001
From: Copilot <198982749+Copilot@users.noreply.github.com>
Date: Tue, 7 Jul 2026 07:53:15 -0700
Subject: [PATCH 3/5] Align SYSLIB diagnostics docs with runtime for
 SYSLIB1223/1225-1229 and add missing SYSLIB0063 (#54661)

* Initial plan

* Update undocumented SYSLIB diagnostics for source generators and obsoletions

* Add SYSLIB0063 to tools diagnostics TOC

* Apply suggestion from @gewarren

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Genevieve Warren <24882762+gewarren@users.noreply.github.com>
---
 .../obsoletions-overview.md                   |  1 +
 .../source-generator-overview.md              | 12 ++---
 .../syslib-diagnostics/syslib0063.md          | 50 +++++++++++++++++++
 .../syslib-diagnostics/syslib1220-1229.md     | 10 ++--
 docs/navigate/tools-diagnostics/toc.yml       |  2 +
 5 files changed, 64 insertions(+), 11 deletions(-)
 create mode 100644 docs/fundamentals/syslib-diagnostics/syslib0063.md

diff --git a/docs/fundamentals/syslib-diagnostics/obsoletions-overview.md b/docs/fundamentals/syslib-diagnostics/obsoletions-overview.md
index 7497bacaee2e6..ff3a063f8b50a 100644
--- a/docs/fundamentals/syslib-diagnostics/obsoletions-overview.md
+++ b/docs/fundamentals/syslib-diagnostics/obsoletions-overview.md
@@ -87,6 +87,7 @@ The following table lists the `SYSLIB0XXX` obsoletions in .NET 5+.
 | [SYSLIB0060](syslib0060.md) | Warning | Constructors on <xref:System.Security.Cryptography.Rfc2898DeriveBytes?displayProperty=nameWithType> are obsolete. Use <xref:System.Security.Cryptography.Rfc2898DeriveBytes.Pbkdf2*?displayProperty=nameWithType> instead. |
 | [SYSLIB0061](syslib0061.md) | Warning | The `Queryable` <xref:System.Linq.Queryable.MaxBy``2(System.Linq.IQueryable{``0},System.Linq.Expressions.Expression{System.Func{``0,``1}},System.Collections.Generic.IComparer{``0})?displayProperty=nameWithType> and <xref:System.Linq.Queryable.MinBy``2(System.Linq.IQueryable{``0},System.Linq.Expressions.Expression{System.Func{``0,``1}},System.Collections.Generic.IComparer{``0})?displayProperty=nameWithType> taking an `IComparer<TSource>` are obsolete. Use the new ones that take an `IComparer<TKey>`. |
 | [SYSLIB0062](syslib0062.md) | Warning | <xref:System.Xml.Xsl.XsltSettings.EnableScript?displayProperty=nameWithType> is obsolete. |
+| [SYSLIB0063](syslib0063.md) | Warning | The <xref:System.IO.Pipes.NamedPipeClientStream> constructor that has an `isConnected` parameter is obsolete because the argument has no effect. Use the constructor that accepts `direction`, `isAsync`, and `safePipeHandle`. |
 | [SYSLIB0064](syslib0064.md) | Warning | <xref:System.Security.Cryptography.RSACryptoServiceProvider.Encrypt(System.Byte[],System.Boolean)?displayProperty=nameWithType> and <xref:System.Security.Cryptography.RSACryptoServiceProvider.Decrypt(System.Byte[],System.Boolean)?displayProperty=nameWithType> are obsolete. Use the overloads that accept an <xref:System.Security.Cryptography.RSAEncryptionPadding> instead. |
 | [SYSLIB0065](syslib0065.md) | Warning | The `set` accessor of <xref:System.Security.Cryptography.AsnEncodedData.RawData?displayProperty=nameWithType> is obsolete. Use the constructor of the appropriate type to decode data, or use <xref:System.Security.Cryptography.AsnEncodedData.CopyFrom(System.Security.Cryptography.AsnEncodedData)?displayProperty=nameWithType> for mutable scenarios. |
 
diff --git a/docs/fundamentals/syslib-diagnostics/source-generator-overview.md b/docs/fundamentals/syslib-diagnostics/source-generator-overview.md
index d87e55d3fdfa7..a6cf1f53d3ef0 100644
--- a/docs/fundamentals/syslib-diagnostics/source-generator-overview.md
+++ b/docs/fundamentals/syslib-diagnostics/source-generator-overview.md
@@ -160,13 +160,13 @@ The following table provides an index to the `SYSLIB1XXX` diagnostics in .NET 6
 | [SYSLIB1220][1220] | JsonSourceGenerator encountered a [JsonConverterAttribute] with an invalid type argument. |
 | [SYSLIB1221][1221] | JsonSourceGenerator does not support this C# language version. |
 | [SYSLIB1222][1222] | Constructor annotated with JsonConstructorAttribute is inaccessible. |
-| [SYSLIB1223][1223] | Constructor annotated with JsonConstructorAttribute is inaccessible. |
+| [SYSLIB1223][1223] | Attributes deriving from JsonConverterAttribute are not supported by the source generator. |
 | [SYSLIB1224][1224] | Types annotated with JsonSerializableAttribute must be classes deriving from JsonSerializerContext. |
-| [SYSLIB1225][1225] | (Reserved for System.Text.Json.SourceGeneration.) |
-| [SYSLIB1226][1226] | (Reserved for System.Text.Json.SourceGeneration.) |
-| [SYSLIB1227][1227] | (Reserved for System.Text.Json.SourceGeneration.) |
-| [SYSLIB1228][1228] | (Reserved for System.Text.Json.SourceGeneration.) |
-| [SYSLIB1229][1229] | (Reserved for System.Text.Json.SourceGeneration.) |
+| [SYSLIB1225][1225] | Type includes a ref-like property, a field, or a constructor parameter. |
+| [SYSLIB1226][1226] | `JsonIgnoreCondition.Always` is not valid on type-level `JsonIgnoreAttribute` annotations. |
+| [SYSLIB1227][1227] | Union case types cannot be unambiguously classified by JSON value type. |
+| [SYSLIB1228][1228] | Union type shape is not a valid C# union. |
+| [SYSLIB1229][1229] | Open generic derived type could not be resolved for the polymorphic base type. |
 | [SYSLIB1230][1230] | Deriving from a `GeneratedComInterface`-attributed interface defined in another assembly is not supported. |
 
 <!-- Include adds ## Suppress warnings (H2 heading) -->
diff --git a/docs/fundamentals/syslib-diagnostics/syslib0063.md b/docs/fundamentals/syslib-diagnostics/syslib0063.md
new file mode 100644
index 0000000000000..c0e37b697e280
--- /dev/null
+++ b/docs/fundamentals/syslib-diagnostics/syslib0063.md
@@ -0,0 +1,50 @@
+---
+title: SYSLIB0063 warning - NamedPipeClientStream constructor with isConnected is obsolete
+description: Learn about the obsoletion of the NamedPipeClientStream constructor that includes an isConnected argument. Use of this constructor generates compile-time warning SYSLIB0063.
+ms.date: 07/06/2026
+ai-usage: ai-assisted
+f1_keywords:
+  - SYSLIB0063
+---
+
+# SYSLIB0063: NamedPipeClientStream constructor with isConnected is obsolete
+
+Starting in .NET 11, the <xref:System.IO.Pipes.NamedPipeClientStream.%23ctor(System.IO.Pipes.PipeDirection,System.Boolean,System.Boolean,Microsoft.Win32.SafeHandles.SafePipeHandle)?displayProperty=nameWithType> constructor is obsolete. Calling this constructor in code generates warning `SYSLIB0063` at compile time.
+
+## Reason for obsoletion
+
+The `isConnected` argument on this constructor has no effect. To avoid confusion, use the constructor that omits this argument.
+
+## Workaround
+
+Use <xref:System.IO.Pipes.NamedPipeClientStream.%23ctor(System.IO.Pipes.PipeDirection,System.Boolean,Microsoft.Win32.SafeHandles.SafePipeHandle)?displayProperty=nameWithType> instead.
+
+## Suppress a warning
+
+If you must use the obsolete API, you can suppress the warning in code or in your project file.
+
+To suppress only a single violation, add preprocessor directives to your source file to disable and then re-enable the warning.
+
+```csharp
+// Disable the warning.
+#pragma warning disable SYSLIB0063
+
+// Code that uses obsolete API.
+// ...
+
+// Re-enable the warning.
+#pragma warning restore SYSLIB0063
+```
+
+To suppress all the `SYSLIB0063` warnings in your project, add a `<NoWarn>` property to your project file.
+
+```xml
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+   ...
+   <NoWarn>$(NoWarn);SYSLIB0063</NoWarn>
+  </PropertyGroup>
+</Project>
+```
+
+For more information, see [Suppress warnings](obsoletions-overview.md#suppress-warnings).
diff --git a/docs/fundamentals/syslib-diagnostics/syslib1220-1229.md b/docs/fundamentals/syslib-diagnostics/syslib1220-1229.md
index aeb2af99514bf..e1d3c7ff89b69 100644
--- a/docs/fundamentals/syslib-diagnostics/syslib1220-1229.md
+++ b/docs/fundamentals/syslib-diagnostics/syslib1220-1229.md
@@ -25,8 +25,8 @@ The following table shows the diagnostic IDs for System.Text.Json source-generat
 |  `SYSLIB1222` | Constructor annotated with `JsonConstructorAttribute` is inaccessible. |
 |  `SYSLIB1223` | Attributes deriving from `JsonConverterAttribute` are not supported by the source generator. |
 |  `SYSLIB1224` | Types annotated with `JsonSerializableAttribute` must be classes deriving from `JsonSerializerContext`. |
-|  `SYSLIB1225` | Type includes `ref` like property, field, or constructor parameter. |
-|  `SYSLIB1226` | Reserved for System.Text.Json.SourceGeneration. |
-|  `SYSLIB1227` | Reserved for System.Text.Json.SourceGeneration. |
-|  `SYSLIB1228` | Reserved for System.Text.Json.SourceGeneration. |
-|  `SYSLIB1229` | Reserved for System.Text.Json.SourceGeneration. |
+|  `SYSLIB1225` | Type includes a ref-like property, a field, or a constructor parameter. |
+|  `SYSLIB1226` | `JsonIgnoreCondition.Always` is not valid on type-level `JsonIgnoreAttribute` annotations. |
+|  `SYSLIB1227` | Union case types cannot be unambiguously classified by JSON value type. |
+|  `SYSLIB1228` | Union type shape is not a valid C# union. |
+|  `SYSLIB1229` | Open generic derived type could not be resolved for the polymorphic base type. |
diff --git a/docs/navigate/tools-diagnostics/toc.yml b/docs/navigate/tools-diagnostics/toc.yml
index d5ceb222cd3a3..fe01b6dfeb346 100644
--- a/docs/navigate/tools-diagnostics/toc.yml
+++ b/docs/navigate/tools-diagnostics/toc.yml
@@ -4091,6 +4091,8 @@ items:
             href: ../../fundamentals/syslib-diagnostics/syslib0061.md
           - name: SYSLIB0062
             href: ../../fundamentals/syslib-diagnostics/syslib0062.md
+          - name: SYSLIB0063
+            href: ../../fundamentals/syslib-diagnostics/syslib0063.md
           - name: SYSLIB0064
             href: ../../fundamentals/syslib-diagnostics/syslib0064.md
           - name: SYSLIB0065

From b5018fbfcbf866afec926776c850bb7dbefbb20d Mon Sep 17 00:00:00 2001
From: Copilot <198982749+Copilot@users.noreply.github.com>
Date: Tue, 7 Jul 2026 11:07:04 -0400
Subject: [PATCH 4/5] Document .runtimeconfig.dev.json `configProperties`
 precedence change in .NET 11 (#54643)

* Initial plan

* Document runtimeconfig.dev configProperties precedence change

* Refine wording for runtimeconfig precedence docs

* Adjust precedence docs phrasing for style guidance

* Update docs/core/runtime-config/index.md

* Update docs/core/compatibility/deployment/11/runtimeconfigdev-configproperties-precedence.md

Co-authored-by: Bill Wagner <wiwagn@microsoft.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Genevieve Warren <24882762+gewarren@users.noreply.github.com>
Co-authored-by: Bill Wagner <wiwagn@microsoft.com>
---
 docs/core/compatibility/11.md                 |  6 ++
 ...meconfigdev-configproperties-precedence.md | 74 +++++++++++++++++++
 docs/core/compatibility/toc.yml               |  4 +
 docs/core/runtime-config/index.md             |  4 +
 4 files changed, 88 insertions(+)
 create mode 100644 docs/core/compatibility/deployment/11/runtimeconfigdev-configproperties-precedence.md

diff --git a/docs/core/compatibility/11.md b/docs/core/compatibility/11.md
index 554f327f2b3d5..5a974af91ea77 100644
--- a/docs/core/compatibility/11.md
+++ b/docs/core/compatibility/11.md
@@ -42,6 +42,12 @@ See [Breaking changes in ASP.NET Core 11](/aspnet/core/breaking-changes/11/overv
 | [API obsoletions](cryptography/11/obsolete-apis.md)            | Source incompatible |
 | [DSA removed from macOS](cryptography/11/dsa-removed-macos.md) | Behavioral change |
 
+## Deployment
+
+| Title | Type of change    |
+|-------|-------------------|
+| [configProperties in .runtimeconfig.dev.json override .runtimeconfig.json](deployment/11/runtimeconfigdev-configproperties-precedence.md) | Behavioral change |
+
 <!--
 ## Entity Framework Core
 
diff --git a/docs/core/compatibility/deployment/11/runtimeconfigdev-configproperties-precedence.md b/docs/core/compatibility/deployment/11/runtimeconfigdev-configproperties-precedence.md
new file mode 100644
index 0000000000000..dcdc6741189be
--- /dev/null
+++ b/docs/core/compatibility/deployment/11/runtimeconfigdev-configproperties-precedence.md
@@ -0,0 +1,74 @@
+---
+title: "Breaking change: configProperties in .runtimeconfig.dev.json override .runtimeconfig.json"
+description: "Learn about the breaking change in .NET 11 where configProperties in .runtimeconfig.dev.json override matching configProperties in .runtimeconfig.json."
+ms.date: 07/05/2026
+ai-usage: ai-assisted
+---
+
+# configProperties in .runtimeconfig.dev.json override .runtimeconfig.json
+
+If an app defines the same runtime `configProperties` key in both `.runtimeconfig.json` and `.runtimeconfig.dev.json`, the `.runtimeconfig.dev.json` value takes precedence.
+
+## Version introduced
+
+.NET 11 Preview 6
+
+## Previous behavior
+
+Previously, `.runtimeconfig.json` took precedence over `.runtimeconfig.dev.json` for duplicate `configProperties` keys.
+
+For example:
+
+```json
+// app.runtimeconfig.json
+{
+  "runtimeOptions": {
+    "configProperties": {
+      "System.GC.Concurrent": true
+    }
+  }
+}
+```
+
+```json
+// app.runtimeconfig.dev.json
+{
+  "runtimeOptions": {
+    "configProperties": {
+      "System.GC.Concurrent": false
+    }
+  }
+}
+```
+
+With this configuration, the runtime used `System.GC.Concurrent: true`.
+
+## New behavior
+
+To support development-time overrides in .NET 11, `.runtimeconfig.dev.json` takes precedence over `.runtimeconfig.json` for duplicate `configProperties` keys.
+
+Using the same example, the runtime now uses `System.GC.Concurrent: false`.
+
+## Type of breaking change
+
+This change is a [behavioral change](../../categories.md#behavioral-change).
+
+## Reason for change
+
+This change enables developers to override production settings during development without modifying production configuration files.
+
+For more information, see [dotnet/runtime#126606](https://github.com/dotnet/runtime/issues/126606).
+
+## Recommended action
+
+For predictable production behavior, only place development-time overrides in `.runtimeconfig.dev.json`.
+
+To prevent a development-time override, remove the duplicate key from `.runtimeconfig.dev.json`.
+
+## Affected APIs
+
+None.
+
+## See also
+
+- [.NET runtime configuration settings](../../../runtime-config/index.md)
diff --git a/docs/core/compatibility/toc.yml b/docs/core/compatibility/toc.yml
index 88869b0c91be1..9d1da27463472 100644
--- a/docs/core/compatibility/toc.yml
+++ b/docs/core/compatibility/toc.yml
@@ -40,6 +40,10 @@ items:
                 href: cryptography/11/obsolete-apis.md
               - name: DSA removed from macOS
                 href: cryptography/11/dsa-removed-macos.md
+          - name: Deployment
+            items:
+              - name: configProperties in .runtimeconfig.dev.json override .runtimeconfig.json
+                href: deployment/11/runtimeconfigdev-configproperties-precedence.md
           - name: Extensions
             items:
               - name: IHost.RunAsync and IHost.StopAsync throw when a BackgroundService fails
diff --git a/docs/core/runtime-config/index.md b/docs/core/runtime-config/index.md
index c9731772ed343..d86822b87bf5b 100644
--- a/docs/core/runtime-config/index.md
+++ b/docs/core/runtime-config/index.md
@@ -39,6 +39,10 @@ Specify runtime configuration options in the **configProperties** section of the
 }
 ```
 
+Starting in .NET 11, to support development-time overrides, the value in *[appname].runtimeconfig.dev.json* takes precedence when you define the same key in `configProperties` in both *[appname].runtimeconfig.dev.json* and *[appname].runtimeconfig.json*.
+
+For more information, see [configProperties in .runtimeconfig.dev.json override .runtimeconfig.json](../compatibility/deployment/11/runtimeconfigdev-configproperties-precedence.md).
+
 ### Example [appname].runtimeconfig.json file
 
 If you're placing the options in the *output* JSON file, nest them under the `runtimeOptions` property.

From 9149a2072823a893d38d47a737284416caa6e1a8 Mon Sep 17 00:00:00 2001
From: Copilot <198982749+Copilot@users.noreply.github.com>
Date: Tue, 7 Jul 2026 11:38:19 -0400
Subject: [PATCH 5/5] Preserve closing XML tag in raw string literal snippet
 output (#54651)

* Initial plan

* fix raw string indentation snippet output

* use block comment for raw string output sample

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
---
 .../strings/snippets/raw-string-literals/Program.cs       | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/docs/csharp/fundamentals/strings/snippets/raw-string-literals/Program.cs b/docs/csharp/fundamentals/strings/snippets/raw-string-literals/Program.cs
index 97500c11eec1c..7e6538dc10a9c 100644
--- a/docs/csharp/fundamentals/strings/snippets/raw-string-literals/Program.cs
+++ b/docs/csharp/fundamentals/strings/snippets/raw-string-literals/Program.cs
@@ -67,9 +67,11 @@ private static void ShowIndentation()
 
         // First content line begins at column 0 of the value:
         Console.WriteLine(xml);
-        // <order id="42">
-        //     <item>book</item>
-        // </order>
+        /* Output:
+           <order id="42">
+               <item>book</item>
+           </order>
+         */
         // </Indentation>
     }