If heading already has a anchor, keep that one instead of creating a new one

[stevemarksd]

I prefer to manually create the anchors.

## [Title 3](#title-2)

your code will mark it as #title-3 in the toc, breaking the whole thing :)

[wooorm]

Please do not delete issue templates. They help us help you. It again shows an enormous lack of appreciation of our time.

This project takes existing IDs.

remark-slug doesn’t overwrite existing IDs.

rehype-slug does not overwrite existing IDs either.

You are creating a link to title-2. Not an ID. GitHub creates a title-3 anchor too.