Clarify recommendations regarding .mjs

src/features/dynamic-import.md

@@ -42,7 +42,7 @@ Here’s how to statically import and use the `./utils.mjs` module:
 ```
 
 :::note
-**Note:** The previous example uses the `.mjs` extension to signal that it’s a module rather than a regular script. On the web, file extensions don’t really matter, as long as the files are served with the correct MIME type (e.g. `text/javascript` for JavaScript files) in the `Content-Type` HTTP header. The `.mjs` extension is [especially useful](https://github.com/nodejs/node-eps/blob/master/002-es-modules.md#32-determining-if-source-is-an-es-module) on other platforms such as Node.js, where there’s no concept of MIME types or other mandatory hooks such as `type="module"` to determine whether something is a module or a regular script. We’re using the same extension here for consistency across platforms and to clearly make the distinction between modules and regular scripts.
+**Note:** The previous example uses the `.mjs` extension to signal that it’s a module rather than a regular script. On the web, file extensions don’t really matter, as long as the files are served with the correct MIME type (e.g. `text/javascript` for JavaScript files) in the `Content-Type` HTTP header. The `.mjs` extension is especially useful on other platforms such as [Node.js](https://nodejs.org/api/esm.html#esm_enabling) and [`d8`](/docs/d8), where it’s a convenient way to indicate to the runtime that your code is a module. We’re using the same extension here for consistency across platforms and to clearly make the distinction between modules and regular scripts.
 :::
 
 This syntactic form for importing modules is a *static* declaration: it only accepts a string literal as the module specifier, and introduces bindings into the local scope via a pre-runtime “linking” process. The static `import` syntax can only be used at the top-level of the file.

src/features/modules.md

@@ -126,13 +126,16 @@ Another difference relates to the `async` attribute, which causes the script to
 
 You may have noticed we’re using the `.mjs` file extension for modules. On the Web, the file extension doesn’t really matter, as long as the file is served with [the JavaScript MIME type `text/javascript`](https://html.spec.whatwg.org/multipage/scripting.html#scriptingLanguages:javascript-mime-type). The browser knows it’s a module because of the `type` attribute on the script element.
 
-Still, we recommend using the `.mjs` extension for modules, for two reasons:
+In production, you should name your files with an `.mjs` extension only if you are sure that they will be served with the required `Content-Type: text/javascript` header. If your host lacks such support, or if you are publishing open source JavaScript for public use by others, it’s safer to use the `.js` extension.
 
-1. During development, it makes it crystal clear that the file is a module as opposed to a regular script. (It’s not always possible to tell just by looking at the code.) As mentioned before, modules are treated differently than regular scripts, so the difference is hugely important!
-1. It’s consistent with Node.js, where [the experimental modules implementation](https://nodejs.org/api/esm.html) only supports files with the `.mjs` extension by default.
+During development, we recommend using the `.mjs` extension for modules, for two reasons:
+
+1. The `.mjs` extension makes it crystal clear to you and anyone else looking at your project that the file is a module as opposed to a regular script. (It’s not always possible to tell just by looking at the code.) As mentioned before, modules are treated differently than regular scripts, so the difference is hugely important!
+
+1. It ensures that your file is parsed as a module by runtimes such as [Node.js](https://nodejs.org/api/esm.html#esm_enabling) and [`d8`](/docs/d8), and build tools such as [Babel](https://babeljs.io/docs/en/options#sourcetype). While these environments and tools each have proprietary ways via configuration to interpret `.js` files as modules, the `.mjs` extension is the cross-compatible way to ensure that files are treated as modules.
 
 :::note
-**Note:** To deploy `.mjs` on the web, your web server needs to be configured to serve files with this extension using the appropriate `Content-Type: text/javascript` header, as mentioned above. Additionally, you may want to configure your editor to treat `.mjs` files as `.js` files to get syntax highlighting. Most modern editors already do this by default.
+**Note:** You may want to configure your editor to treat `.mjs` files as `.js` files to get syntax highlighting. Most modern editors already do this by default.
 :::
 
 ### Module specifiers { #specifiers }