Syntax Highlighting Breaks with Frontmatter

[Lakuna]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)

Affected packages and versions

MDX v1.8.9

Link to runnable example

No response

Steps to reproduce

As of today (potentially related to the new Visual Studio Code update 1.92, which came out yesterday), MDX files with frontmatter don't display proper syntax highlighting.

1. Create a file and use MDX syntax highlighting.
2. Add frontmatter to the file.
3. Write standard MDX content below the frontmatter.

I am using Node.js version 22.3.0.

Expected behavior

The standard syntax highlighting should appear (this was the case for me until today).

Actual behavior

The entire file is highlighted as if it were YAML.

Runtime

Other (please specify in steps to reproduce)

Package manager

npm v10

OS

Windows

Build and bundle tools

Next.js

[remcohaszing]

Duplicate of wooorm/markdown-tm-language#10

[remcohaszing]

But it is interesting to know this was caused by VSCode 1.92.