Can custom floats work with compact syntax?

[d-morrison]

Description

I'm wondering whether there's a way to make the following qmd add the Figure S#: label to the first caption:

---
title: "test"
format: html
crossref:
  custom:
    - kind: float
      key: suppfig
      reference-prefix: Figure S
      space-before-numbering: false
---


```{r}
#| label: suppfig-fig1
#| fig-cap: "a figure"
plot(1:10)
```

::: {#suppfig-fig2}

```{r}
#| fig-cap: "another figure"
plot(10:1)
```

:::

Currently, the first figure doesn't get a caption label:

[cscheid]

It won't be an easy thing to change, because it will require us to teach knitr about custom crossrefs. The syntax we would support would be something like

```{r}
#| label: suppfig-fig1
#| suppfig-cap: "a figure"
plot(1:10)
```

But don't hold your breath, this is a harder change than it appears.

[cderv]

Issue to follow on this is this one

• Teach engine about new custom crossref #7665