core/release-notes/5.0/api-diff/netstandard2.1/5.0_System.Runtime.Versioning.md

System.Runtime.Versioning

 namespace System.Runtime.Versioning {
+    public abstract class OSPlatformAttribute : Attribute {
+        public string PlatformName { get; }
+    }
+    public sealed class SupportedOSPlatformAttribute : OSPlatformAttribute {
+        public SupportedOSPlatformAttribute(string platformName);
+    }
+    public sealed class TargetPlatformAttribute : OSPlatformAttribute {
+        public TargetPlatformAttribute(string platformName);
+    }
+    public sealed class UnsupportedOSPlatformAttribute : OSPlatformAttribute {
+        public UnsupportedOSPlatformAttribute(string platformName);
+    }
 }