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

(WIP)

# foo {#id}

vs

1 + 1 = {1 + 1}

The language server in the MDX extension for VS Code show a syntax error on the header syntax.
I believe the current syntax using single braces is no longer approved.
Double parens ((#id)) is an alternative.

Reproducible demo

WIP

Steps to reproduce

1. Enable the language server
2. Add a header with its ID

Expected behavior

No errors

Actual behavior

Syntax error

Your environment

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

WIP

Self-service

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