**Background**
Other extensions can register tags to be syntax highlighted wherever CodeMirror is used. This is done using [[ https://www.mediawiki.org/wiki/Manual:Extension_registration#Attributes | extension attributes ]], whereby in an extension.json, you can specify `CodeMirrorTagModes` with an object having the tag name as the key, and the value being the MIME content type for which we want syntax highlighted. For example, the Cite extension registers its `<ref>` tag to be highlighted with [[ https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Cite/+/348673/5/extension.json | like the following ]]:
```lang=json
"CodeMirrorTagModes": {
"ref": "text/mediawiki"
}
```
This task is to track the work that goes into making this system work in CodeMirror 6, which is [[ https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules | JavaScript module-based ]] (as opposed to CommonJS-style that ResourceLoader supports).
**Acceptance criteria**
* Any extension that supplies a `CodeMirrorTagModes` for `text/mediawiki` (or just `mediawiki`) should highlight the specified tag, and highlight the contents therein like normal wikitext.
* Support for languages other than MediaWiki wikitext will be saved for a separate task, and likewise for PluginModules.