docs: Publish v9.21.0 release highlights

src/content/blog/2025-02-21-eslint-v9.21.0-released.md

@@ -3,18 +3,35 @@ layout: post
 title: ESLint v9.21.0 released
 teaser: "We just pushed ESLint v9.21.0, which is a minor release upgrade of ESLint. This release adds some new features and fixes several bugs found in the previous release."
 image: release-notes-minor.png
-draft: true
 authors:
-  - eslintbot
+  - fasttime
 categories:
   - Release Notes
 tags:
   - Release
 ---
 
 
+## Highlights
 
+### `--ext` CLI Option
 
+This version of ESLint reintroduces the command line option `--ext` to allow linting files with a particular extension.
+The `--ext` option has always been available in the legacy "eslintc" configuration system, but it was eliminated in the new configuration system because its functionality can be easily achieved through [`files`](/docs/latest/use/configure/configuration-files#specifying-files-and-ignores) patterns.
+For example, specifying `files: ["**/*.ts"]` in a configuration object will lint all files that have the `.ts` extension.
+`files` patterns are useful to lint files with extensions other than `.js`, `.mjs` or `.cjs`, but they require a configuration file. In order to lint files with arbitrary extensions without a configuration file, the `--ext` option can now be used in the command line like this:
+
+```shell
+npx eslint --no-config-lookup --rule '{"no-unused-vars": "error"}' --ext '.jsx'
+```
+
+See the [CLI documentation](/docs/latest/use/command-line-interface#--ext) for further information.
+
+### New Metadata for Deprecated Rules
+
+ESLint v9.21.0 extends the format of rule metadata to better annotate deprecated rules, providing more detailed information.
+This includes the specific version of a plugin in which a rule was deprecated, as well as links to alternative rules and plugins.
+[Learn more](/docs/latest/extend/rule-deprecation).