net10.0-windows10.0.22621 
namespace System.Windows.Markup
{
    [AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = true)]
    public sealed class MarkupExtensionReturnTypeAttribute : Attribute
    {
        [Obsolete("The expressionType argument is not used by the XAML parser. To specify the expected return type, use MarkupExtensionReturnTypeAttribute(Type). To specify custom handling for expression types, use XamlSetMarkupExtensionAttribute.")]
        public MarkupExtensionReturnTypeAttribute(Type returnType, Type expressionType);
    }
}
.NET
5.06.07.08.09.010.0
.NET Core
3.03.1
.NET Framework
3.54.04.54.5.14.5.24.64.6.14.6.24.74.7.14.7.24.84.8.1
Information specific to net10.0
Platforms This API is only available when you target a specific platform:
Windows
7.08.010.0.1776310.0.1836210.0.1904110.0.2034810.0.2200010.0.22621
Information specific to net10.0-windows10.0.22621
Assembly

System.Xaml , Version=10.0.0.0, PublicKeyToken=b77a5c561934e089

Referencing

Your project needs to set <UseWPF>True</UseWPF>.

Obsolete The expressionType argument is not used by the XAML parser. To specify the expected return type, use MarkupExtensionReturnTypeAttribute(Type). To specify custom handling for expression types, use XamlSetMarkupExtensionAttribute.
Platform Restrictions

This API is only supported on the following platforms:

  • Windows
  • Built-in API
  • Package-provided API