Typst: option to shrink wide display equations to the text width

[faysou]

A display equation wider than the text area extends into the margin and past the page edge in Typst output.

---
format: typst
---

$$
a_1 + a_2 + a_3 + a_4 + a_5 + a_6 + a_7 + a_8 + a_9 + a_{10} + a_{11} + a_{12} + a_{13} + a_{14} + a_{15} + a_{16} + a_{17} + a_{18} + a_{19} + a_{20} + a_{21} + a_{22}
$$

The last term ends at x = 594pt on a 612pt-wide page.

Proposal

An opt-in document option that shrinks display equations wider than the text area to fit, for example with scale inside layout. Shrinking changes the font size of the equation, so I don't think it should be the default.

Would an option like this be accepted, and is there a preferred name and place for it, such as under typst format options?

[mcanouil]

Thanks for the clear example.

Wide display equations have come up before in other formats, which is probably where the overlap is:

• How to have long equations scrollable on smaller screens? #9248: scrolling long equations in HTML with overflow-x: auto on mjx-container[display="true"].
• Automatic column width for latex equations in html page #2170: an equation wider than the column in HTML, which is a MathJax limitation (an extension is suggested there).
• malformated table in revealjs when long equation with $\sqrt$ is used #13485: a long equation with \sqrt distorting a table in Reveal.js.

None of them cover Typst, so this case is still open.

For Typst you can get shrink-to-fit today with a show rule in include-in-header:

---
format:
  typst:
    include-in-header:
      - text: |
          #show math.equation.where(block: true): it => layout(size => context {
            let w = measure(it).width
            if w > size.width { scale(size.width / w * 100%, reflow: true, it) } else { it }
          })
---

layout gives the available width, measure gives the equation width, and scale with reflow: true shrinks only the equations that are too wide.
Equations that fit keep their font size.
I tried it on your example with a numbered equation ({#eq-w}) and a short equation: the wide one fits the text width with its number, and the short one is unchanged.

This is only my opinion, not a maintainer decision.
I think this is better left as a user-side snippet than added as a Quarto option, because it is a few lines of Typst and shrinking is not always what people want (some would prefer a line break).
The earlier HTML threads were settled the same way.