How to only make level 3 Slides vertical.

[seapat]

Description

Hey,

I was wondering if there is some workaround to let # and ## both denote horizontal slides and use only ### for vertical slides. The slide-level option does put ## and ### on the same slides if set to 2. Here is an example:

# (horizontal) Section heading

## Horizontal slide A

### Vertical slide A1

### Vertical slide A2

## Horizontal slide B

[mcanouil]

No, that's not how Pandoc thus Quarto works. 🤷‍♂️

[mcanouil]

I doubled check, the Lua would need to replace what Quarto/Pandoc do when replacing headers by nested sections.

See https://revealjs.com/vertical-slides/ and https://pandoc.org/MANUAL.html#structuring-the-slide-show.

Note: in reveal.js slide shows, if slide level is 2, a two-dimensional layout will be produced, with level-1 headings building horizontally and level-2 headings building vertically. It is not recommended that you use deeper nesting of section levels with reveal.js unless you set --slide-level=0 (which lets reveal.js produce a one-dimensional layout and only interprets horizontal rules as slide boundaries).

[cscheid]

I must be missing something. The idea would be to use a Lua filter to find the Header 3 elements that the user wrote, and then emit something else that is properly interpreted by Pandoc. This is a general technique in writing filters: if the output is possible to generate with a different input, then you write a Lua filter to convert the "wrong" input from the user into the input that is expected by Pandoc.

So the idea isn't to change how Pandoc works. It's to convert what the user wrote into what Pandoc is expecting.

[mcanouil]

I might be also missing something ...

Let's write it down^^

• change the default direction to vertical
  • h1 behave as horizontal section -> section not nested.
  • h2 behave as vertical section -> section nested.
  • h3 not a slide separator (with slide-level: 2) -> added in the parent section

Now, the Lua filter would need to:

1. turn h2 into h1
2. turn h3 into h2

But I am not convinced it would work.

[cscheid]

I just tested this, it works:

---
title: "Presentation"
format:
  revealjs:
    navigation-mode: vertical
filters:
  - relevel_headings.lua
---

# (horizontal) Section heading

## Horizontal slide A

### Vertical slide A1

### Vertical slide A2

## Horizontal slide B

relevel_headings.lua:

function Header(heading)
  if heading.level == 3 then
    heading.level = 2
    return heading
  elseif heading.level == 2 then
    heading.level = 1
    return heading
  end
  return heading
end

[cscheid]

Ok, I think your point is that in this way, the slides are actually "sections", and that's true. But the horizontal/vertical navigation works as expected.

[mcanouil]

Yep, I also just tried the filter^^

It's really not an intuitive use of Reveal.js structure (independently of how Pandoc uses markdown to creates the HTML sections).

[cderv]

What I am not sure to understand here is that

• You are transforming ### to ##
• You are transforming ## to #
• You are leaving # untouched

So basically, Using this Lua filter is equivalent to write directly

# (horizontal) Section heading

# Horizontal slide A

## Vertical slide A1

## Vertical slide A2

# Horizontal slide B
```

Is this really what we want here ? This is useful for a presentation where wouldn't want to change level in `.qmd` source (because in HTML , the tags and styling will not be the level from the markdown as we change it). 

I would say, no Lua filter is needed to create vertical slides, just only using two levels of headers in document is simpler !

Though `slide-level` can help, but with different results...  

`revealjs` format with Pandoc works on two level only. Especially for vertical slides: 
* One level for Sections slides, which will be horizontal
* Other levels (above `slide-level`) will be used as vertical

This means that 
```markdown
---
title: "Presentation"
format:
  revealjs:
    navigation-mode: vertical
    slide-level: 3
---

# (horizontal) Section heading

## Horizontal slide A

### Vertical slide A1

### Vertical slide A2

## Horizontal slide B
```

Would work for `###` to create some slides. 

However, only one level can be used as horizontal slide by Pandoc. 

* `#` will do horizontal slide
* `##` will do vertical 
* `###` will do vertical too

This is why the note they shared as stated in above comment https://github.com/quarto-dev/quarto-cli/discussions/5853#discussioncomment-6126290

Using `navigation-mode: linear` (our default) will make a 1D layout of slides which `#`, `##` and `###` all creating slides. 

So overall, when using vertical slides, solutions is to use only two levels I guess! 

[mcanouil]

@cderv The use of level 3 puzzled me as well 😅
The only useful thing that the various level brings is an IDE feature, i.e., you have more fine grained control on parts you want to collapse.

PS: there is some code blocks delimitation issues in your post.