1 files changed, 67 insertions, 0 deletions
diff --git a/third_party/rust/ron/docs/extensions.md b/third_party/rust/ron/docs/extensions.md
new file mode 100644
index 0000000000..ae648d778a
--- /dev/null
+++ b/third_party/rust/ron/docs/extensions.md
@@ -0,0 +1,67 @@
+## RON extensions
+
+RON has extensions that can be enabled by adding the following attribute at the top of your RON document:
+
+`#![enable(...)]`
+
+# unwrap_newtypes
+
+You can add this extension by adding the following attribute at the top of your RON document:
+
+`#![enable(unwrap_newtypes)]`
+
+This feature enables RON to automatically unwrap simple tuples.
+
+```rust
+struct NewType(u32);
+struct Object {
+    pub new_type: NewType,
+}
+```
+
+Without `unwrap_newtypes`, because the value `5` can not be saved into `NewType(u32)`, your RON document would look like this:
+
+``` ron
+(
+    new_type: (5),
+)
+```
+
+With the `unwrap_newtypes` extension, this coercion is done automatically. So `5` will be interpreted as `(5)`.
+
+``` ron
+#![enable(unwrap_newtypes)]
+(
+    new_type: 5,
+)
+```
+
+# implicit_some
+
+You can add this extension by adding the following attribute at the top of your RON document:
+
+`#![enable(implicit_some)]`
+
+This feature enables RON to automatically convert any value to `Some(value)` if the deserialized struct requires it.
+
+```rust
+struct Object {
+    pub value: Option<u32>,
+}
+```
+
+Without this feature, you would have to write this RON document.
+
+```ron
+(
+    value: Some(5),
+)
+```
+
+Enabling the feature would automatically infer `Some(x)` if `x` is given. In this case, RON automatically casts this `5` into a `Some(5)`.
+
+```ron
+(
+    value: 5,
+)
+```