This supports forwarding types to the runtime including CustomAttributeExtensions, InterfaceMapping and RuntimeReflectionExtensions.
This package was used in the past to expose common functionality across different runtimes in a uniform way. It continues to ship as part of the shared framework, but it is frozen for compatibility.
System.Reflection.Extensions is included in the shared framework. The package does not need to be installed into any project compatible with .NET Standard 2.0.