guardrex · Jul 15, 2026 · Jul 8, 2026 · Jul 8, 2026 · Jul 9, 2026 · Jul 9, 2026
@@ -1,11 +1,12 @@
 ---
 title: Dynamically-rendered ASP.NET Core Razor components
+ai-usage: ai-assisted
 author: guardrex
 description: Learn how to use dynamically-rendered Razor components in Blazor apps.
 monikerRange: '>= aspnetcore-6.0'
 ms.author: wpickett
 ms.custom: mvc
-ms.date: 11/11/2025
+ms.date: 07/10/2026
 uid: blazor/components/dynamiccomponent
 ---
 # Dynamically-rendered ASP.NET Core Razor components
@@ -252,6 +253,120 @@ In the following example:
 
 :::moniker-end
 
+:::moniker range=">= aspnetcore-11.0"
+
+Dictionary values for [C# union-typed parameters](/dotnet/csharp/language-reference/builtin-types/union) must be boxed as the union, not the raw case value, because an implicit conversion is only valid at compile-time.
+
+<!-- UPDATE 11.0 - Remove the NOTE at GA -->
+
+> [!NOTE]
+> During the preview of .NET 11, the following example requires the app's project file to specify the "`preview`" C# language version:
+>
+> ```xml
+> <LangVersion>preview</LangVersion>
+> ```
+
+Consider the following C# union type, `SlotContent`, that accepts text, a <xref:Microsoft.AspNetCore.Components.MarkupString>, or a <xref:Microsoft.AspNetCore.Components.RenderFragment>:
+
+```csharp
+using Microsoft.AspNetCore.Components;
+
+public union SlotContent(string, MarkupString, RenderFragment);
+```
+
+The following `Slot` component exposes a component parameter typed to the `SlotContent` union and renders the union's content using two implementations of the [C# `switch` expression](/dotnet/csharp/language-reference/operators/switch-expression), one through an assignment to a <xref:Microsoft.AspNetCore.Components.RenderFragment> (`ContentSwitch`) and one via an inline `switch` expression. In the following example, the [`[EditorRequired]` attribute](xref:Microsoft.AspNetCore.Components.EditorRequiredAttribute) specifies that `Content` is a required component parameter at design-time or build-time.
+
+`Slot.razor`:
+
+```razor
+<h2>@@ContentSwitch</h2>
+
+<div>
+    @ContentSwitch()
+</div>
+
+<h2>Inline <code>switch</code> expression</h2>
+
+<div>
+    @switch (Content)
+    {
+        case string text:
+            @text
+            break;
+        case MarkupString html:
+            @html
+            break;
+        case RenderFragment fragment:
+            @fragment
+            break;
+        default:
+            <em>Empty slot!</em>
+            break;
+    }
+</div>
+
+@code {
+    [Parameter, EditorRequired] 
+    public SlotContent Content { get; set; }
+
+    private RenderFragment ContentSwitch() => Content switch
+    {
+        string text => @<span>@text</span>,
+        MarkupString html => @<span>@html</span>,
+        RenderFragment fragment => fragment,
+        _ => @<em>Empty slot!</em>
+    };
+}
+```
+
+<span aria-hidden="true">❌</span><span class="visually-hidden">Unsupported:</span> Using the preceding `Slot` component, the following component fails at run time with an <xref:System.InvalidCastException>:
+
+```razor
+@page "/slot-test-1"
+
+<DynamicComponent Type="@TargetComponent" Parameters="@BadParameters" />
+
+@code {
+    [Parameter]
+    public Type TargetComponent { get; set; } = typeof(Slot);
+
+    [Parameter]
+    public string RawTextPayload { get; set; } = "Hello from dynamic data!";
+
+    private Dictionary<string, object> BadParameters => new()
+    {
+        { "Content", RawTextPayload }
+    };
+}
+```
+
+> :::no-loc text="System.InvalidCastException: Unable to cast object of type 'System.String' to type 'SlotContent'.":::
+
+<span aria-hidden="true">✔️</span><span class="visually-hidden">Supported:</span> To box the union, wrap the raw value explicitly into the union wrapper type (`new SlotContent(...)`), as the following example demonstrates.
+
+`SlotTest2.razor`:
+
+```razor
+@page "/slot-test-2"
+
+<DynamicComponent Type="@TargetComponent" Parameters="@ValidParameters" />
+
+@code {
+    [Parameter]
+    public Type TargetComponent { get; set; } = typeof(Slot);
+
+    [Parameter]
+    public string RawTextPayload { get; set; } = "Hello from dynamic data!";
+
+    private Dictionary<string, object> ValidParameters => new()
+    {
+        { "Content", new SlotContent(RawTextPayload) }
+    };
+}
+```
+
+:::moniker-end
+
 ## Event callbacks (`EventCallback`)
 
 Event callbacks (<xref:Microsoft.AspNetCore.Components.EventCallback>) can be passed to a <xref:Microsoft.AspNetCore.Components.DynamicComponent> in its parameter dictionary.

@@ -1,11 +1,12 @@
 ---
 title: ASP.NET Core Razor components
+ai-usage: ai-assisted
 author: guardrex
 description: Learn how to create and use Razor components in Blazor apps, including guidance on Razor syntax, component naming, namespaces, and component parameters.
 monikerRange: '>= aspnetcore-3.1'
 ms.author: wpickett
 ms.custom: mvc
-ms.date: 06/24/2026
+ms.date: 07/10/2026
 uid: blazor/components/index
 ---
 # ASP.NET Core Razor components
@@ -850,14 +851,6 @@ Assign a C# field, property, or result of a method to a component parameter as a
 
 If the component parameter is of type string, then the attribute value is instead treated as a C# string literal. If you want to specify a C# expression instead, then use the `@` prefix.
 
-:::moniker range=">= aspnetcore-11.0"
-
-<!-- UPDATE 11.0 - Remove the following paragraph per resolution of the PU issue -->
-
-The string-literal shortcut applies only to parameters declared as `string`. A parameter declared as a [C# union type](/dotnet/csharp/whats-new/csharp-14#union-types), even one whose cases include `string`, isn't a `string`-typed parameter, so the attribute value must be a C# expression. Use the `@` prefix, for example `Message="@("Saved.")"`.
-
-:::moniker-end
-
 The following parent component displays four instances of the preceding `ParameterChild` component and sets their `Title` parameter values to:
 
 * The value of the `title` field.
@@ -1171,6 +1164,122 @@ Quote &copy;2005 [Universal Pictures](https://www.uphe.com): [Serenity](https://
 
 :::moniker-end
 
+:::moniker range=">= aspnetcore-11.0"
+
+Support for [C# union types](/dotnet/csharp/language-reference/builtin-types/union) allows a single component parameter to represent a value that's exactly one of a fixed set of types with compiler-enforced exhaustive pattern matching. A component parameter is set by direct assignment when a component is rendered from Razor markup or through <xref:Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder.AddComponentParameter%2A?displayProperty=nameWithType>.
+
+<!-- UPDATE 11.0 - Remove the NOTE at GA -->
+
+> [!NOTE]
+> During the preview of .NET 11, the following example requires the app's project file to specify the "`preview`" C# language version:
+>
+> ```xml
+> <LangVersion>preview</LangVersion>
+> ```
+
+The following C# union type, `SlotContent`, accepts text, a <xref:Microsoft.AspNetCore.Components.MarkupString>, or a <xref:Microsoft.AspNetCore.Components.RenderFragment>:
+
+```csharp
+using Microsoft.AspNetCore.Components;
+
+public union SlotContent(string, MarkupString, RenderFragment);
+```
+
+The following `Slot` component exposes a component parameter typed to the `SlotContent` union and renders the union's content using two implementations of the [C# `switch` expression](/dotnet/csharp/language-reference/operators/switch-expression), one through an assignment to a <xref:Microsoft.AspNetCore.Components.RenderFragment> (`ContentSwitch`) and one via an inline `switch` expression. In the following example, the [`[EditorRequired]` attribute](xref:Microsoft.AspNetCore.Components.EditorRequiredAttribute) specifies that `Content` is a required component parameter at design-time or build-time.
+
+`Slot.razor`:
+
+```razor
+<h2>@@ContentSwitch</h2>
+
+<div>
+    @ContentSwitch()
+</div>
+
+<h2>Inline <code>switch</code> expression</h2>
+
+<div>
+    @switch (Content)
+    {
+        case string text:
+            @text
+            break;
+        case MarkupString html:
+            @html
+            break;
+        case RenderFragment fragment:
+            @fragment
+            break;
+        default:
+            <em>Empty slot!</em>
+            break;
+    }
+</div>
+
+@code {
+    [Parameter, EditorRequired] 
+    public SlotContent Content { get; set; }
+
+    private RenderFragment ContentSwitch() => Content switch
+    {
+        string text => @<span>@text</span>,
+        MarkupString html => @<span>@html</span>,
+        RenderFragment fragment => fragment,
+        _ => @<em>Empty slot!</em>
+    };
+}
+```
+
+The following `SlotExample` component uses the preceding `SlotContent` type and `Slot` component.
+
+`SlotExample.razor`:
+
+```razor
+@page "/slot-example"
+
+<h1>Plain text</h1>
+
+<Slot Content="@("Simple plain text slot")" />
+
+<h1><code>MarkupString</code></h1>
+
+<Slot Content='@((MarkupString)"<strong>Bold HTML slot</strong>")' />
+
+<h1><code>RenderFragment</code></h1>
+
+<Slot Content="@content" />
+
+@code {
+    private SlotContent content;
+
+    protected override void OnInitialized()
+    {
+        content = new SlotContent((RenderFragment)(b =>
+        {
+            b.OpenElement(0, "button");
+            b.AddAttribute(1, "onclick", EventCallback.Factory.Create(this, Increment));
+            b.AddContent(2, "Count: ");
+            b.AddContent(3, currentCount);
+            b.CloseElement();
+        }));
+    }
+
+    private int currentCount = 0;
+
+    private void Increment() => currentCount++;
+}
+```
+
+<!-- UPDATE 11.0 - Remove the following paragraph per resolution of the PU issue -->
+
+The string-literal shortcut applies only to parameters declared as `string`. A parameter declared as a C# union type, even one whose cases include `string`, isn't a `string`-typed parameter, so the attribute value must be a C# expression. Use the `@` prefix, as demonstrated by `Content="@("Simple plain text slot")"` in the preceding example.
+
+<!-- UPDATE 13.0 - Remove the following cross-link when C# unions get some time on them (target removal for .NET 13) -->
+
+For more information, see [Explore union types in C# 15](https://devblogs.microsoft.com/dotnet/csharp-15-union-types/).
+
+:::moniker-end
+
 ## Route parameters
 
 Components can specify route parameters in the route template of the [`@page`][9] directive. The [Blazor router](xref:blazor/fundamentals/routing) uses route parameters to populate corresponding component parameters.

@@ -855,7 +855,7 @@ The correct culture-invariant formatting is applied for the given type (<xref:Sy
 :::moniker range=">= aspnetcore-11.0"
 
 > [!NOTE]
-> [C# union types](/dotnet/csharp/whats-new/csharp-14#union-types) aren't supported by `[SupplyParameterFromQuery]` or `[SupplyParameterFromForm]`, which bind string or form values without JSON parsing.
+> [C# union types](/dotnet/csharp/language-reference/builtin-types/union) aren't supported by `[SupplyParameterFromQuery]` or `[SupplyParameterFromForm]`, which bind string or form values without JSON parsing.
 
 :::moniker-end
 

@@ -362,7 +362,7 @@ When the [`OnInitialized{Async}` lifecycle method](xref:blazor/components/lifecy
 :::moniker range=">= aspnetcore-11.0"
 
 > [!NOTE]
-> Route parameters can't be typed as a [C# union](/dotnet/csharp/whats-new/csharp-14#union-types). The router parses route segments as strings and converts them to the target type without JSON parsing, so it can't dispatch to a union case.
+> Route parameters can't be typed as a [C# union](/dotnet/csharp/language-reference/builtin-types/union). The router parses route segments as strings and converts them to the target type without JSON parsing, so it can't dispatch to a union case.
 
 :::moniker-end
 

@@ -5,7 +5,7 @@ description: Learn how to invoke .NET methods from JavaScript functions in Blazo
 monikerRange: '>= aspnetcore-3.1'
 ms.author: wpickett
 ms.custom: mvc, sfi-ropc-nochange
-ms.date: 11/11/2025
+ms.date: 07/09/2026
 uid: blazor/js-interop/call-dotnet-from-javascript
 ---
 # Call .NET methods from JavaScript functions in ASP.NET Core Blazor
@@ -22,6 +22,16 @@ This article explains how to invoke .NET methods from JavaScript (JS).
 
 For information on how to call JS functions from .NET, see <xref:blazor/js-interop/call-javascript-from-dotnet>.
 
+:::moniker range=">= aspnetcore-11.0"
+
+<!-- UPDATE 13.0 - Consider removing the following cross-link because the 'call JS from .NET' article
+                   will maintain a versioned support remark beyond .NET 13. -->
+
+> [!NOTE]
+> [C# union types](/dotnet/csharp/language-reference/builtin-types/union) are supported.
+
+:::moniker-end
+
 ## Invoke a static .NET method
 
 To invoke a static .NET method from JavaScript (JS), use the JS functions:

@@ -5,7 +5,7 @@ description: Learn how to invoke JavaScript functions from .NET methods in Blazo
 monikerRange: '>= aspnetcore-3.1'
 ms.author: wpickett
 ms.custom: mvc, sfi-ropc-nochange
-ms.date: 11/11/2025
+ms.date: 07/09/2026
 uid: blazor/js-interop/call-javascript-from-dotnet
 ---
 # Call JavaScript functions from .NET methods in ASP.NET Core Blazor
@@ -26,12 +26,28 @@ For information on how to call .NET methods from JS, see <xref:blazor/js-interop
 
 For the preceding .NET methods that invoke JS functions:
 
+:::moniker range=">= aspnetcore-11.0"
+
 * The function identifier (`String`) is relative to the global scope (`window`). To call `window.someScope.someFunction`, the identifier is `someScope.someFunction`. There's no need to register the function before it's called.
 * Pass any number of JSON-serializable arguments in `Object[]` to a JS function.
 * The cancellation token (`CancellationToken`) propagates a notification that operations should be canceled.
 * `TimeSpan` represents a time limit for a JS operation.
 * The `TValue` return type must also be JSON serializable. `TValue` should match the .NET type that best maps to the JSON type returned.
 * A [JS `Promise`](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Promise) is returned for `InvokeAsync` methods. `InvokeAsync` unwraps the [`Promise`](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Promise) and returns the value awaited by the [`Promise`](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Promise).
+* [C# union types](/dotnet/csharp/language-reference/builtin-types/union) are supported.
+
+:::moniker-end
+
+:::moniker range="< aspnetcore-11.0"
+
+* The function identifier (`String`) is relative to the global scope (`window`). To call `window.someScope.someFunction`, the identifier is `someScope.someFunction`. There's no need to register the function before it's called.
+* Pass any number of JSON-serializable arguments in `Object[]` to a JS function.
+* The cancellation token (`CancellationToken`) propagates a notification that operations should be canceled.
+* `TimeSpan` represents a time limit for a JS operation.
+* The `TValue` return type must also be JSON serializable. `TValue` should match the .NET type that best maps to the JSON type returned.
+* A [JS `Promise`](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Promise) is returned for `InvokeAsync` methods. `InvokeAsync` unwraps the [`Promise`](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Promise) and returns the value awaited by the [`Promise`](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Promise).
+
+:::moniker-end
 
 For Blazor apps with prerendering enabled, which is the default for server-side apps, calling into JS isn't possible during prerendering. For more information, see the [Prerendering](#prerendering) section.
 

@@ -6,7 +6,7 @@ description: Learn how to persist user data (state) in Blazor apps using Blazor'
 monikerRange: '>= aspnetcore-8.0'
 ms.author: wpickett
 ms.custom: mvc
-ms.date: 11/11/2025
+ms.date: 07/09/2026
 uid: blazor/state-management/prerendered-state-persistence
 ---
 # ASP.NET Core Blazor prerendered state persistence
@@ -143,6 +143,17 @@ In the following example that serializes state for multiple components of the sa
 }
 ```
 
+:::moniker-end
+
+:::moniker range=">= aspnetcore-11.0"
+
+> [!NOTE]
+> A user-configured <xref:System.Text.Json.Serialization.JsonSerializerContext> doesn't flow into [C# union](/dotnet/csharp/language-reference/builtin-types/union) deserialization. Instead, use `[JsonUnion(TypeClassifier = typeof({TYPE CLASSIFIER}))]`, where the `{TYPE CLASSIFIER}` placeholder is the type classifier.
+
+:::moniker-end
+
+:::moniker range=">= aspnetcore-10.0"
+
 ## Serialize state for services
 
 In the following example that serializes state for a dependency injection service: