--slide-level in reveal.js presentation has a weird behaviour

[pagdot]

Pandoc Version 2.5

In my experience the slide-level paramter doesn't alsways work as intended and sometimes has a really weird behaviour.

This issue is not about content getting dropped!

Example 1

Example markdown:

---
title: Breaking slide levels
author: Paul Götzinger
revealjs-url: https://cdnjs.cloudflare.com/ajax/libs/reveal.js/3.7.0/
---

# Header 1

## Header 2

### Header 3

### Header 3

Command used to create html:

pandoc -s -t revealjs --slide-level 1 .\slides.md -o .\slides.html -V revealjs-url=https://cdnjs.cloudflar
e.com/ajax/libs/reveal.js/3.7.0/

I only change the slide level in the command.

Slide level 1

Only top-level slides. Works as intended.

Slide level 2

Header 1 gets converted to a section, Header 2 gets converted to a slide. Works as intended

Slide level 3

Same output as with --slide-level 2. Does not work as intended.

Example 2

Example markdown:

---
title: Breaking slide levels
author: Paul Götzinger
revealjs-url: https://cdnjs.cloudflare.com/ajax/libs/reveal.js/3.7.0/
---

# Header 1

### Header 3

### Header 3

Command used to create html:

pandoc -s -t revealjs --slide-level 1 .\slides.md -o .\slides.html -V revealjs-url=https://cdnjs.cloudflar
e.com/ajax/libs/reveal.js/3.7.0/

I only change the slide level in the command.

Slide level 1

Only top-level slides. Works as intended.

Slide level 2

Because Header 2 is not available it somehow breaks the presentation and the content overlays the section slide:

Does really not work as intended.

Slide level 3

Header 1 gets converted to a section, Header 3 gets converted to a slide. Works as intended

[mb21]

Have you seen http://pandoc.org/MANUAL.html#structuring-the-slide-show ? Especially:

Content above the slide level will not appear in the slide show.

[pagdot]

Have you seen http://pandoc.org/MANUAL.html#structuring-the-slide-show ? Especially:

Content above the slide level will not appear in the slide show.

Yes. My issue isn't related to missing content. Under certain conditions the Slide level seems to be ignored (Example 1, slide level 3) or if no matching header is found the content should be at least truncated and not overlay the section

[jgm]

It would be helpful if you could look at the HTML structure pandoc produces with these options and say how you think it should be revised. reveal.js is a bit different from the other formats because of the 2D structure.

[pagdot]

I have looked at it again and compared the HTML structure. I've copied only relevant HTML code without title slide and formatted it to understand it easier.

Example 1

Slide level 2

<section>
    <section id="header-1" class="title-slide slide level1">
        <h1>Header 1</h1>
    </section>
    <section id="header-2" class="slide level2">
        <h2>Header 2</h2>
        <h3 id="header-3-1">Header 3-1</h3>
        <h3 id="header-3-2">Header 3-2</h3>
    </section>
</section>

Slide level 3

<section>
    <section id="header-1" class="title-slide slide level1">
        <h1>Header 1</h1>
    </section>
    <section>
        <section id="header-2" class="title-slide slide level2">
            <h2>Header 2</h2>
        </section>
        <section id="header-3-1" class="slide level3">
            <h3>Header 3-1</h3>
        </section>
        <section id="header-3-2" class="slide level3">
            <h3>Header 3-2</h3>
        </section>
    </section>
</section>

Pandoc seem to add a higher depth to sections than supported which causes issues with side generation and content placement.

Slide level 3 revised

According to the documentation of --slide-level i rearranged the slides and slide levels.

<section>
    <section id="header-1" class="title-slide slide level1">
        <h1>Header 1</h1>
    </section>
</section>
<section>
    <section id="header-2" class="title-slide slide level2">
        <h2>Header 2</h2>
    </section>
    <section id="header-3-1" class="slide level3">
        <h3>Header 3-1</h3>
    </section>
    <section id="header-3-2" class="slide level3">
        <h3>Header 3-2</h3>
    </section>
</section>

Example 2

Slide level 1

<section id="header-1" class="slide level1">
    <h1>Header 1</h1>
    <h3 id="header-3">Header 3</h3>
    <h3 id="header-3-1">Header 3</h3>
</section>

Slide level 2

<section>
    <section id="header-1" class="title-slide slide level1">
        <h1>Header 1</h1>
    </section>
    <h3 id="header-3">Header 3</h3>
    <h3 id="header-3-1">Header 3</h3>
</section>

Because the given slide level doesn't match any header, the truncation of worng placed content seem to be missing.

Slide level 2 revised

According to the documentation of --slide-level i truncated the wrong placed contet.

<section>
    <section id="header-1" class="title-slide slide level1">
        <h1>Header 1</h1>
    </section>
</section>

[jgm]

Example 2 isn't a real problem. The level 3 headers are below the slide level, so they're considered part of the slide. They shouldn't be truncated. (Sorry, I missed that you tried it also with --slide-level=2. I agree that the output here is broken, though it's not a huge concern, since it's probably only by mistake that someone would specify --slide-level=2 here. I think the best thing would be not to truncate the level 3 headers, but to include them on a titleless slide. They do need to be wrapped in a <section>, though.)

In Example 1 there may be a real issue with --slide-level=3, since reveal.js apparently expects at most 2 levels of section element nesting, and we provide more. Your suggested output seems like a good approach.

[fernandezcuesta]

Hi,
before this commit the following markdown:

---
title: my slides
author: me
date: 1 Jan 2019
---

# Slide title
#### section header

## second level
content

## yet another slide
more content

# Second section
#### second section header

## etc
etc

was being rendered as a set of vertical slides with a common header (i.e. section header). This behaviour was lost since 2.6, I guess as a side effect of this fix.