Update metadata.md

[internetisaiah]

Pull Request/Issue Resolution

Description of Change:

Realized that the original description is the exact opposite of what is actually happening lol. i.e. toc_headers doesn't hide the listed headings, it hides non-listed headings.

If my updated wording is still clunky, feel free to offer an edit as (to me) it's a little awkward to explain so I'm not sure if I did a great job haha.

Is this change associated with a Braze feature/product release?

• Yes (Insert Feature Release Date Here)
• No

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[bre-fitzgerald]

Oop, didn't fully read your PR description at first 😅 To make this easier to read, I would rephrase to state what it does do, not what it doesn't do. Added a suggested edit to that effect!