Prism Quarto Extension

The prism filter lets a single Div, Span, or CodeBlock carry conditional attributes: each output format picks its own values from format-prefixed keys, so the same prose or code can be styled differently in HTML, revealjs, and Typst without duplication.

Attributes are keyed format:name="value". At render time, attributes whose format matches the active output are re-emitted as name="value"; the rest are dropped. Unprefixed attributes pass through unchanged.

How prefixes resolve

Prism matches each prefix against the target format of the current render, resolved from quarto.format.format_identifier()["target-format"]. Matching is exact, so html: targets HTML output without affecting revealjs.

This document is rendered to three formats:

Format-scoped attributes on Divs

Each prefix is independent: html:style is applied only under HTML, revealjs:style only under revealjs, and typst:fill only under Typst. The unprefixed note attribute is preserved everywhere.

::: {
  note="kept everywhere"
  html:style="color: hotpink;"
  revealjs:style="color: deepskyblue;"
  typst:fill='rgb("#b22222")'
}
This paragraph is pink in HTML, blue in revealjs, and unstyled in Typst.
:::

Override behaviour

A format-scoped attribute overrides a static attribute of the same name. Under HTML the html: value wins; under revealjs the revealjs: value wins; under Typst no prefix matches, so the static gray is kept.

::: {
  style="color: gray;"
  html:style="color: rebeccapurple;"
  revealjs:style="color: forestgreen;"
}
This paragraph reads as purple in HTML, green in revealjs, and gray in Typst.
:::

Format-scoped attributes on Spans

Inline content carries format-scoped attributes the same way.

The next sentence styles a
[single span]{html:style="background: yellow; padding: 0 0.2em;" revealjs:style="background: lightyellow; padding: 0 0.2em;"}
only under the matching format.

The next sentence styles a single span only under the matching format.

Format-scoped attributes on CodeBlocks

CodeBlocks accept the same syntax.

```{
  .r
  html:style="background: #f6f8fa; padding: 0.5em;"
  revealjs:style="background: #1f2937; color: #e5e7eb; padding: 0.5em;"
}
1 + 1
```

1 + 1

Unmatched prefixes are dropped

Prefixes that do not resolve to the active target format are removed entirely. The next Div carries only revealjs: and typst: attributes; under HTML it therefore renders as plain content with no style attribute.

::: {revealjs:style="color: indigo;" typst:fill='rgb("#0d9488")'}
Plain content in HTML; styled in revealjs and Typst.
:::

Format-group aliases

The slide alias matches every HTML slide format: revealjs, slidy, s5, dzslides, and slideous. A single slide: prefix targets the whole group, so the next Div is styled under revealjs without naming each slide format. Under HTML and Typst no slide format is active, so the slide: value is dropped.

::: {slide:style="color: chocolate;"}
Styled under any HTML slide format; plain in HTML and Typst.
:::

An exact format prefix wins over the slide alias for the same attribute name. Under revealjs the revealjs: value applies; under any other slide format the slide: value would apply instead.

::: {slide:style="color: teal;" revealjs:style="color: crimson;"}
Crimson under revealjs, teal under the other slide formats.
:::

Default fallback

A default:name prefix provides a fallback value, applied only when no format-specific variant of the same name matched the active format. Under HTML the html: value wins; under revealjs and Typst no specific variant matches, so the default: value is used.

::: {default:style="color: gray;" html:style="color: rebeccapurple;"}
Purple under HTML, gray under revealjs and Typst.
:::