Some metadata set in `_metadata.yml` and in YAML header inside document are not correctly merged.

Discussed in https://github.com/quarto-dev/quarto-cli/discussions/9855

^{Originally posted by McKabue June 3, 2024}

/posts/welcome/index.qmd

---
title: "Welcome To My Blog"
date: "2024-05-01"
categories: [news]
author: "martin from welcome"
---

This is the first post in a Quarto blog. Welcome!

![](thumbnail.jpg)

Since this post doesn't specify an explicit `image`, the first image in the post will be used in the listing page of posts.

/posts/_metadata.yml

categories: [tech]
author:
  - name: James from posts

With the above setup, I get the following post and listing:

However, if:

/posts/welcome/index.qmd

---
title: "Welcome To My Blog"
date: "2024-05-01"
---

This is the first post in a Quarto blog. Welcome!

![](thumbnail.jpg)

Since this post doesn't specify an explicit `image`, the first image in the post will be used in the listing page of posts.

/posts/welcome/_metadata.yml

categories: [news]
author: "martin from welcome"

/posts/_metadata.yml

categories: [tech]
author:
  - name: James from posts

I get the following post and listing:

When the metadata is in the document file, it overwrites all parent metadata such as authors and categories instead of extending it in the post page.