diff --git a/index.js b/index.js
index 1ba9dc1..d72322d 100644
--- a/index.js
+++ b/index.js
@@ -1,6 +1,6 @@
 /**
- * @typedef {import('bcp-47').Options} Options
  * @typedef {import('bcp-47').Warning} Warning
+ * @typedef {import('./lib/index.js').Options} Options
  */
 
 export {bcp47Normalize} from './lib/index.js'
diff --git a/lib/index.js b/lib/index.js
index fe1e71b..99608e9 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -4,8 +4,20 @@
  * @typedef {import('bcp-47').Extension} Extension
  *
  * @typedef Options
+ *   Configuration (optional).
  * @property {boolean} [forgiving]
+ *   Passed to `bcp-47` as `options.forgiving`.
  * @property {Warning} [warning]
+ *   Passed to `bcp-47` as `options.warning`.
+ *
+ *   One additional warning is given:
+ *
+ *   | code | reason                                                     |
+ *   | :--- | :--------------------------------------------------------- |
+ *   | 7    | Deprecated region `CURRENT`, expected one of `SUGGESTIONS` |
+ *
+ *   This warning is only given if the region cannot be automatically fixed
+ *   (when regions split into multiple regions).
  */
 
 import {parse, stringify} from 'bcp-47'
diff --git a/readme.md b/readme.md
index 74aa322..c6875ae 100644
--- a/readme.md
+++ b/readme.md
@@ -38,7 +38,7 @@ to normalize and clean them.
 ## Install
 
 This package is [ESM only][esm].
-In Node.js (version 12.20+, 14.14+, or 16.0+), install with [npm][]:
+In Node.js (version 14.14+, 16.0+), install with [npm][]:
 
 ```sh
 npm install bcp-47-normalize
@@ -96,7 +96,7 @@ zh-hans-cn -> zh
 
 ## API
 
-This package exports the following identifier: `bcp47Normalize`.
+This package exports the identifier `bcp47Normalize`.
 There is no default export.
 
 ### `bcp47Normalize(tag[, options])`
@@ -128,13 +128,12 @@ Normal, canonical, and pretty [BCP 47][spec] tag (`string`).
 ## Types
 
 This package is fully typed with [TypeScript][].
-It exports additional `Options` and `Warning` types that model their respective
-interfaces.
+It exports the additional types `Options` and `Warning`.
 
 ## Compatibility
 
 This package is at least compatible with all maintained versions of Node.js.
-As of now, that is Node.js 12.20+, 14.14+, and 16.0+.
+As of now, that is Node.js 14.14+ and 16.0+.
 It also works in Deno and modern browsers.
 
 ## Security