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docs: add note about escaping heading IDs #11783

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12 changes: 12 additions & 0 deletions website/docs/guides/markdown-features/markdown-features-toc.mdx
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Expand Up @@ -87,6 +87,18 @@ For MDX files, the `{#id}` syntax should be avoided. Since Docusaurus v3 and MDX

:::

:::tip Escaping heading IDs
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@slorber slorber Mar 6, 2026

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Work in underway regarding heading ids, see recent PRs

As the warning above says, you should avoid this syntax with MDX now.

In practice, the markdown.mdx1Compat.headingIds option automatically escapes, so my proposal would be to update the warning above to mention manual escaping is also possible

It is only supported in Docusaurus for backward compatibility, thanks to the markdown.mdx1Compat.headingIds config option, or by manually escaping the JSX expression: \{#id}


If your heading text contains a `{#` sequence that you don't want to be interpreted as a custom heading ID, you can escape it with a backslash:

```md
### Hello World \{#not-an-id}
```

This will render the heading text as-is, including the `{#not-an-id}` part, instead of treating it as a custom ID.

:::

:::warning Avoid colliding IDs

Generated heading IDs will be guaranteed to be unique on each page, but if you use custom IDs, make sure each one appears exactly once on each page, or there will be two DOM elements with the same ID, which is invalid HTML semantics, and will lead to one heading being unlinkable.
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