fix(typst): prevent breaking inside definition items

[mcanouil]

Ensure terms and their descriptions remain together by preventing breaks within definition items.

The rule needs to be separate from the content rule, because here we play on the implicit block generated by Typst.

As this is a visual change, there are no tests, but I believe non breaking term/definition is a sensible default.

Code	Before	After
--- title: "Quarto Playground" format: typst keep-typ: true --- ## Introduction {{< lipsum 4 >}} Multi-format output : Generate HTML, PDF, Word, ePub, and more from one source.

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[gordonwoodhull]

I added a test using ensurePdfTextPositions. Without the fix, it reports

Cannot compare positions: "Generate HTML" is on page 2, "Multi-format" is on page 1    

[cderv]

Thank you!

I see this is added in definitions.typ and concerns Definition block which is a Pandoc blocks initially.

Would that be worth also making a PR in Pandoc for this fix to be upstream too ?

[mcanouil]

The terms rule is already different from Pandoc, should it be part of the PR?

• https://github.com/jgm/pandoc/blob/893a00bcc25a3adad5772f1eff1bd5171d241187/data/templates/default.typst#L3-L10

Edit: in fact the rule is incompatible with how Pandoc writes terms definition.
It would be

#show terms: it => {
  it
    .children
    .map(child => block(breakable: false)[
      #text(weight: "bold")[#child.term]
      #block(inset: (left: 1.5em, top: -0.4em))[#child.description]
    ])
    .join()
}

Question is: should we update upstream and use the above rule instead of the two?

[cderv]

I'll let @gordonwoodhull reply. I see it was adapted on our side for PDF accessibility so we need to keep ours, but maybe that would be worth reporting upstream this PDF accessibility improvement then 🤔 Commit: 9525c1b

Keeping our template improvement with upstream is best when we can. And when they don't accept it, then we'll need to patch at each update (and remember why we are different).

[mcanouil]

The rule I'm showing is a mixed between our fix and Pandoc current implementation.
It should (I did not verify though) pass the accessibility check as it's not using #strong().

[cderv]

To be clear, 9525c1b was a switch to what you see in Pandoc's template to a new way that pass PDF accessibility. Are you offering a third way?

I was thinking of sharing this resulting PR code to Pandoc upstream to report

• PDF accessibility improvement
• non-breaking definition list

[mcanouil]

Are you offering a third way?

Yes, one that fits with the two rules. The initial suggestion was a simpler rule as it relied on implicit block, but that's also why it then needed a second rule to change breakable.

[cderv]

Ok so doing

#show terms: it => {
  it
    .children
    .map(child => block(breakable: false)[
      #text(weight: "bold")[#child.term]
      #block(inset: (left: 1.5em, top: -0.4em))[#child.description]
    ])
    .join()
}

would avoid the #show terms.item: set block(breakable: false) ?

@gordonwoodhull what do you think ?

[mcanouil]

Yes, it would

---
title: "Quarto Playground"
format:
  typst:
    keep-typ: true
---

```{=typst}
#show terms: it => {
  it
    .children
    .map(child => block(breakable: false)[
      #text(weight: "bold")[#child.term]
      #block(inset: (left: 1.5em, top: -0.4em))[#child.description]
    ])
    .join()
}
```

## Introduction

{{< lipsum 4 >}}

Multi-format output
: Generate HTML, PDF, Word, ePub, and more from one source.

[gordonwoodhull]

I'm in favor of a unified rule, and contributing upstream. However, you'll want to test with

format:
  typst:
    pdf-standard: ua-1

as the above proposal fails Typst's validation:

[typst]: Compiling definition-item-no-break.typ to definition-item-no-break.pdf...

ERROR: error: PDF/UA-1 error: invalid list (L) structure
    ┌─ tests/docs/smoke-all/typst/definition-item-no-break.typ:382:2
    │
382 │ / Multi-format: #block[
    │   ^^^^^^^^^^^^
    │
    = hint: list (L) may not contain paragraph (P)
    = hint: this is probably caused by a show rule

error: PDF/UA-1 error: invalid list (L) structure
    ┌─ tests/docs/smoke-all/typst/definition-item-no-break.typ:382:0
    │  
382 │ ╭ / Multi-format: #block[
383 │ │ Generate HTML, PDF, Word, ePub, and more from one source.
384 │ │ ]
    │ ╰─^
    │  
    = hint: list (L) may not contain marked content directly
    = hint: this is probably caused by a show rule

It does pass the ensurePdfTextPositions test, and looks visually OK!

Interestingly, the previous code (from this PR) does pass UA-1.

[mcanouil]

New variant that actually does not messed up the list structure as Pandoc code does.
Here we skip directly the parent to directly target the children (items), this way we can change the item content without touching the whole list structure.

#show terms.item: it => block(breakable: false)[
  #text(weight: "bold")[#it.term]
  #block(inset: (left: 1.5em, top: -0.4em))[#it.description]
]

This passed UA-1 Typst validation.

[gordonwoodhull]

Much cleaner! We should definitely upstream this.