The latest yaml validator now complains about the pandoc "title-slide-attributes" keys for the revealjs format. 

Try the following reproducible example:

```{markdown}
---
title: "Habits"
author: "John Doe"
title-slide-attributes:
  data-background-image: "https://via.placeholder.com/300"
  data-background-size: 300px
  data-background-position: 4% 90%
format: revealjs
---

## Getting up

- Get out of bed

![](https://via.placeholder.com/300) 
```
I got complains:
```markdown
ERROR: Validation of YAML front matter failed.
In file title-slide.qmd
(line 5, column 3 through line 7, column 34) Key title-slide-attributes has value data
-background-image: "https://via.placeholder.com/300"
  data-background-size: 300px
  data-background-position: 4% 90% but it must instead be the null value
4: title-slide-attributes:
5:   data-background-image: "https://via.placeholder.com/300"
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
6:   data-background-size: 300px
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
7:   data-background-position: 4% 90%
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
8: format: revealjs
✖ The value data-background-image: "https://via.placeholder.com/300"
  data-background-size: 300px
  data-background-position: 4% 90% is a object.
ℹ The error happened in location title-slide-attributes.
ERROR: Render failed due to invalid YAML.
```

2022-01-30T19:28:33Z
juliantao
closed
revealjs: yml validation on pandoc "title-slide-attributes"
https://github.com/quarto-dev/quarto-cli/issues/297