diff --git a/doc/features.md b/doc/features.md
index 1c0e42c215..08f55b657f 100644
--- a/doc/features.md
+++ b/doc/features.md
@@ -1,6 +1,6 @@
 # Features
 
-## Abstract references ([experimental](usage.md#experimental))
+## Abstract references ([experimental](usage.md#experimental)) ([spec](https://github.com/zenparsing/es-abstract-refs))
 
 ```javascript
 foo::bar;
@@ -39,7 +39,7 @@ var bob = {
 };
 ```
 
-## Async functions ([experimental](usage.md#experimental))
+## Async functions ([experimental](usage.md#experimental)) ([spec](https://github.com/lukehoban/ecmascript-asyncawait))
 
 ```javascript
 async function chainAnimationsAsync(elem, animations) {
diff --git a/lib/6to5/transformation/transformers/abstract-references.js b/lib/6to5/transformation/transformers/abstract-references.js
index e69de29bb2..aa3011ed83 100644
--- a/lib/6to5/transformation/transformers/abstract-references.js
+++ b/lib/6to5/transformation/transformers/abstract-references.js
@@ -0,0 +1 @@
+// https://github.com/zenparsing/es-abstract-refs