format: md front matter doesn't work

[doraeric]

Have you read the Contributing Guidelines on issues?

• I have read the Contributing Guidelines on issues.

Prerequisites

• I'm using the latest version of Docusaurus.
• I have tried the npm run clear or yarn clear command.
• I have tried rm -rf node_modules yarn.lock package-lock.json and re-installing packages.
• I have tried creating a repro with https://new.docusaurus.io.
• I have read the console error message carefully (if applicable).

Description

The docs say that adding format: md front matter makes the doc to be CommonMark format, but it doesn't work.
After looking into the code, it should be

---
mdx:
  format: md
---

It reads the mdx in front matter first

docusaurus/packages/docusaurus-mdx-loader/src/utils.ts

Lines 99 to 105 in a4fa4c2

	const mdxFrontMatter = validateMDXFrontMatter(frontMatter.mdx);
	const processor = await getProcessor({
	filePath,
	options,
	mdxFrontMatter,
	});

docusaurus/packages/docusaurus-mdx-loader/src/processor.ts

Lines 266 to 285 in a4fa4c2

	export async function getProcessor({
	filePath,
	mdxFrontMatter,
	options,
	}: {
	filePath: string;
	mdxFrontMatter: MDXFrontMatter;
	options: Options;
	}): Promise<SimpleProcessor> {
	const processors =
	options.processors ?? (await createProcessorsCacheEntry({options}));
	const format = getFormat({
	filePath,
	frontMatterFormat: mdxFrontMatter.format,
	markdownConfigFormat: options.markdownConfig.format,
	});
	return format === 'md' ? processors.mdProcessor : processors.mdxProcessor;
	}

But the docs say it's format in front matter.

docusaurus/website/docs/guides/markdown-features/markdown-features-react.mdx

Line 251 in a4fa4c2

- The `format: md` front matter

docusaurus/website/docs/guides/markdown-features/markdown-features-intro.mdx

Line 44 in a4fa4c2

It is possible to **opt-in for CommonMark** using the [`siteConfig.markdown.format`](../../api/docusaurus.config.js.mdx#markdown) setting or the `format: md` front matter.

Should it be fixed in the code or in the docs?

Reproducible demo

No response

Steps to reproduce

1. add format: md front matter in .mdx file
2. nothing happened

Expected behavior

Doc changes to CommonMark syntax.

Actual behavior

Doc stay with JSX syntax

Your environment

• Public source code:
• Public site URL:
• Docusaurus version used: v3
• Environment name and version (e.g. Chrome 89, Node.js 16.4):
• Operating system and version (e.g. Ubuntu 20.04.2 LTS):

Self-service

• I'd be willing to fix this bug myself.

[slorber]

Damn, yes you are right 😅

Should it be fixed in the code or in the docs?

Hmmm, I don't know. I'd like to have format: instead of mdx.format but at the same time it's likely that we add extra options under the mdx namespace. I think we should just fix the docs.