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+# Contributing
+
+## Adding a new plugin or polyfill to support (when approved in the next ECMAScript version)
+
+### Update [`plugin-features.js`](https://github.com/babel/babel/blob/main/packages/babel-compat-data/scripts/data/plugin-features.js)
+
+*Example:*
+
+If you were going to add `**` which is in ES2016:
+
+Find the relevant entries on [compat-table](https://kangax.github.io/compat-table/es2016plus/#test-exponentiation_(**)_operator):
+
+`exponentiation (**) operator`
+
+Find the corresponding babel plugin:
+
+`@babel/plugin-transform-exponentiation-operator`
+
+And add them in this structure:
+
+```js
+// es2016
+"@babel/plugin-transform-exponentiation-operator": {
+  features: [
+    "exponentiation (**) operator",
+  ],
+},
+```
+
+### Update data for `core-js@2` polyfilling
+
+*Example:*
+
+In case you want to add `Object.values` which is in ES2017:
+
+Find the relevant feature and subfeature on [compat-table](https://kangax.github.io/compat-table/es2016plus/#test-Object_static_methods_Object.values)
+and split it with `/`:
+
+`Object static methods / Object.values`
+
+Find the corresponding module on [`core-js@2`](https://github.com/zloirock/core-js/tree/v2/modules):
+
+`es7.object.values.js`
+
+Find required ES version in [`corejs2-built-in-features.js`](https://github.com/babel/babel/blob/main/packages/babel-preset-env/data/corejs2-built-in-features.js) and add the new feature:
+
+```js
+const es = {
+  //...
+  "es7.object.values": "Object static methods / Object.values"
+}
+```
+
+If you want to transform a new built-in by `useBuiltIns: 'usage'`, add mapping to related `core-js` modules to [this file](https://github.com/babel/babel/blob/main/packages/babel-preset-env/polyfills/corejs2/built-in-definitions.js).
+
+### Update data for `core-js@3` polyfilling
+
+Just update the version of [`core-js-compat`](https://github.com/zloirock/core-js/tree/main/packages/core-js-compat) in dependencies.
+
+If you want to transform a new built-in by `useBuiltIns: 'usage'`, add mapping to related [`core-js`](https://github.com/zloirock/core-js/tree/main/packages/core-js/modules) modules to [this file](https://github.com/babel/babel/blob/main/packages/babel-preset-env/polyfills/corejs3/built-in-definitions.js).
+
+If you want to mark a new proposal as shipped, add it to [this list](https://github.com/babel/babel/blob/main/packages/babel-preset-env/polyfills/corejs3/shipped-proposals.js).
+
+### Update [`plugins.json`](https://github.com/babel/babel/blob/main/packages/babel-preset-env/data/plugins.json)
+
+Until `compat-table` is a standalone npm module for data we are using the git commit in `packages/babel-compat-data/scripts/download-compat-table.sh`
+
+`COMPAT_TABLE_COMMIT=[latest-commit-hash]`,
+
+So we update and then run `npm run build-data`. If there are no changes, then `plugins.json` will be the same.
+
+## Tests
+
+### Running tests
+See general [CONTRIBUTING.md](https://github.com/babel/babel/blob/main/CONTRIBUTING.md#running-lintingtests).
+
+### Writing tests
+
+#### General
+
+All the tests for `@babel/preset-env` exist in the `test/fixtures` folder. The
+test setup and conventions are exactly the same as testing a Babel plugin, so
+please read our [documentation on writing tests](https://github.com/babel/babel/blob/main/CONTRIBUTING.md#babel-plugin-x).
+
+#### Testing the `debug` option
+
+Testing debug output to `stdout` is similar. Under the `test/debug-fixtures`,
+create a folder with a descriptive name of your test, and add the following:
+
+* Add a `options.json` file (just as the other tests, this is essentially a
+`.babelrc`) with the desired test configuration (required)
+* Add a `stdout.txt` file with the expected debug output. For added
+convenience, if there is no `stdout.txt` present, the test runner will
+generate one for you.