Contains reflection types such as TypeAttributes. Some of these types are forwarded to the runtime. In the future, the non-forwarded types may be lifted to the runtime and then type forwards added.
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.Primitives is included in the shared framework. The package does not need to be installed into any project compatible with .NET Standard 2.0.