docs: virtual modules ID naming convention (#5505)

docs/guide/api-plugin.md

@@ -17,7 +17,7 @@ When learning, debugging, or authoring plugins we suggest including [vite-plugin
 
 ## Conventions
 
-If the plugin doesn't use Vite specific hooks and can be implemented as a [Compatible Rollup Plugin](#rollup-plugin-compatibility), then it is recommended to use the [Rollup Plugin naming conventions](https://rollupjs.org/guide/en/#conventions)
+If the plugin doesn't use Vite specific hooks and can be implemented as a [Compatible Rollup Plugin](#rollup-plugin-compatibility), then it is recommended to use the [Rollup Plugin naming conventions](https://rollupjs.org/guide/en/#conventions) (except for virtual modules naming, see note below).
 
 - Rollup Plugins should have a clear name with `rollup-plugin-` prefix.
 - Include `rollup-plugin` and `vite-plugin` keywords in package.json.
@@ -36,6 +36,10 @@ If your plugin is only going to work for a particular framework, its name should
 - `vite-plugin-react-` prefix for React Plugins
 - `vite-plugin-svelte-` prefix for Svelte Plugins
 
+Rollup recommends prefixing the module ID for 'virtual modules' (e.g. for helper functions) with `\0`. This prevents other plugins from trying to process it. But this convention for paths isn't browser-friendly.
+
+Vite convention for virtual modules is to prefix the path with `virtual:`. If possible the plugin name should be used as a namespace to avoid collisions with other plugins in the ecosystem. For example, a `vite-plugin-posts` could ask users to import a `virtual:posts` or `virtual:posts/helpers` virtual modules to get build time information.
+
 ## Plugins config
 
 Users will add plugins to the project `devDependencies` and configure them using the `plugins` array option.