The `fragment-index` Has No Effect on Images for `Reveal.JS`

Bug description

It seems that Quarto doesn't apply the fragment-index to images:

## How to Measure

::: {.incremental}
- Assume we have 2 variants of a website: `A` and `B`.
- How would we measure their design effect on user engagement?
:::

![](https://i.imgur.com/PSZggyN.png){.absolute bottom=0 .fragment .fade-in-then-out fragment-index=20}

The output will have data-fragment-index=0 for the image.

In the case above I want the image to appear in sync with an item of the list.
So I'd like to be able to have ![](https://i.imgur.com/PSZggyN.png){.absolute bottom=0 .fragment .fade-in-then-out fragment-index=20} yet what ever I do, I can't control its index.

Just as a note, it would be great to be able to have control on the index in .incremental. Maybe something like defining the index of the first item (Then all are chained)?

This is tested on Windows 10, VS Code, Quarto Extension 1.56 and Quarto CLI 1.2.269.

Checklist

• Please include a minimal, fully reproducible example in a single .qmd file? Please provide the whole file rather than the snippet you believe is causing the issue.
• Please format your issue so it is easier for us to read the bug report.
• Please document the RStudio IDE version you're running (if applicable), by providing the value displayed in the "About RStudio" main menu dialog?
• Please document the operating system you're running. If on Linux, please provide the specific distribution.

Start with the minimal .qmd example in the issue and render it as a Reveal.JS presentation using the reported Quarto CLI setup. Inspect the generated output to compare the requested fragment-index=20 with the observed data-fragment-index=0; done means the image receives and honors the requested index while remaining synchronized with the list.