Microsoft.CodeAnalysis.Razor

 {
     namespace Microsoft.CodeAnalysis.Razor {
+        public static class CompilerFeatures {
+            public static void Register(RazorProjectEngineBuilder builder);
+        }
         public sealed class DefaultTagHelperDescriptorProvider : RazorEngineFeatureBase, IRazorEngineFeature, IRazorFeature, ITagHelperDescriptorProvider {
-            public bool DesignTime { get; set; }

         }
+        public static class RazorProjectEngineBuilderExtensions {
+            public static RazorProjectEngineBuilder SetCSharpLanguageVersion(this RazorProjectEngineBuilder builder, LanguageVersion csharpLanguageVersion);
+        }
     }
 }