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.changeset/proud-pigs-know.md

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+---
+'highlightjs-glimmer': minor
+---
+
+Previously, this package enabled glimmer-js support by patching into the official highlightjs javascript grammar. This is problematic if you want to support both gjs and js(/jsx) syntax highlighting alongside each other.
+
+This change refactors things so that glimmer-javascript is defined and exported as a standalone grammar. Instead of patching the standard javascript grammar, it uses the `subLanguage` feature to extend it cleanly. hbs-literal and template-tag support are added via additional 'contains' rules.
+
+To maintain the existing 'override javascript grammar' behavior for existing consumers of this package, the setup APIs will register `javascript`, `js`, `mjs` and `cjs` as aliases of the new `glimmer-javascript` grammar. Consumers who want to take advantage of the standalone grammar can import it and register using the standard `hljs.registerLanguage` technique.
+
+For example:
+
+```js
+import hljs from 'highlight.js';
+import { glimmerJavascript } from 'highlightjs-glimmer';
+
+hljs.registerLanguage('glimmer-javascript', (hljs) => {
+  const definition = glimmerJavascript(hljs, 'glimmer-javascript');
+
+  return definition;
+});
+```
+
+The old usage, `setup` and other methods,
+
+```js
+import hljs from 'highlight.js';
+import { setup } from 'highlightjs-glimmer';
+
+setup(hljs);
+
+hljs.highlightAll();
+```
+
+Has been unchanged in this release, but is likely to change in a major so that the default / recommended APIs don't take away from the possibility of using other languages in the same document.