fix: wrap vcenter mpadded in mrow for valid MathML by cyphercodes · Pull Request #4193 · KaTeX/KaTeX

cyphercodes · 2026-04-05T01:50:27Z

Problem

When \vcenter is used inside \mathrel (and similar commands), the resulting MathML is invalid:

<!-- Before: Invalid MathML -->
<mo><mpadded class="vcenter"\u003e...</mpadded></mo>

The issue is that <mpadded> cannot be a direct child of <mo> per the MathML spec.

Solution

Wrap the <mpadded> element in an <mrow> to produce valid MathML:

<!-- After: Valid MathML -->
<mo><mrow><mpadded class="vcenter">...</mpadded></mrow></mo>

Changes

Modified src/functions/vcenter.ts to wrap mpadded in mrow

Testing

All 1270 existing Jest tests pass
TypeScript compilation passes
Linting passes

Fix invalid MathML structure when \vcenter is used inside \mathrel. Previously, \mathrel{\vcenter{:}} produced <mo><mpadded>...</mpadded></mo>, which is invalid because <mpadded> cannot be a child of <mo>. Now wraps the <mpadded> in an <mrow>, producing valid MathML: <mo><mrow><mpadded>...</mpadded></mrow></mo> Fixes KaTeX#4078

greptile-apps · 2026-04-05T01:54:18Z

Greptile Summary

This PR fixes invalid MathML output when \vcenter is nested inside \mathrel or similar commands (\mathbin, \mathord, etc.), where <mpadded> as a direct child of <mo> is not permitted by the MathML spec. The one-line fix wraps mpadded in mrow, which is semantically neutral (grouping only) and produces spec-compliant output.

Confidence Score: 5/5

Safe to merge; the fix is minimal, correct, and all 1270 existing tests pass.

The change is a targeted two-liner that wraps mpadded in mrow, directly matching the MathML content-model spec. No existing behavior is altered for standalone vcenter usage since mrow is semantically transparent. The only remaining feedback is a P2 suggestion to add a regression test, which does not block merge.

No files require special attention.

Important Files Changed

Filename	Overview
src/functions/vcenter.ts	Wraps mpadded in mrow so vcenter produces valid MathML inside mo/mi/mrel elements; fix is correct and minimal.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["\\mathrel{\\vcenter{...}}"] --> B["mclass mathmlBuilder"]
    B --> C["mo node"]
    C -->|"Before fix"| D["mpadded.vcenter ❌ invalid child of mo"]
    C -->|"After fix"| E["mrow"]
    E --> F["mpadded.vcenter ✓ valid per MathML spec"]

_{Reviews (1): Last reviewed commit: "fix: wrap vcenter mpadded in mrow for va..." | Re-trigger Greptile}

greptile-apps · 2026-04-05T01:54:22Z

+        const mpadded = new MathNode(
            "mpadded", [mml.buildGroup(group.body, options)], ["vcenter"]);
+        return new MathNode("mrow", [mpadded]);


Missing regression test for the fixed scenario

No test currently asserts the MathML structure when \vcenter is nested inside \mathrel (or \mathbin, \mathord, etc.) — the exact bug being fixed. Adding a test that renders \mathrel{\vcenter{\frac{a}{b}}} and checks that the output does not contain <mo><mpadded (bare mpadded inside mo) would guard this path against future regressions.

codecov · 2026-04-05T09:03:01Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.32%. Comparing base (314f856) to head (3fafd5a).
⚠️ Report is 119 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4193      +/-   ##
==========================================
+ Coverage   93.15%   93.32%   +0.16%     
==========================================
  Files          91       91              
  Lines        6795     6812      +17     
  Branches     1582     1585       +3     
==========================================
+ Hits         6330     6357      +27     
- Misses        429      453      +24     
+ Partials       36        2      -34

Files with missing lines	Coverage Δ
src/functions/vcenter.ts	`100.00% <100.00%> (ø)`

... and 15 files with indirect coverage changes

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ed12205...3fafd5a. Read the comment docs.

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

edemaine

As Grigoriy has pointed out, this is potentially suboptimal if \vcenter isn't nested inside something, but I think it's fine to take this simpler approach. I do wonder whether other macros need a similar treatment... but can worry about that another time.

grigoriy-reshetniak · 2026-04-05T13:30:46Z

Thank you!

edemaine · 2026-04-05T13:33:19Z

🎉 This PR is included in version 0.16.45 🎉

The release is available on:

Your semantic-release bot 📦🚀

## [0.16.45](v0.16.44...v0.16.45) (2026-04-05) ### Bug Fixes * wrap vcenter mpadded in mrow for valid MathML ([#4193](#4193)) ([ee66b78](ee66b78)), closes [#4078](#4078)

This PR contains the following updates: | Package | Change | [Age](https://docs.renovatebot.com/merge-confidence/) | [Confidence](https://docs.renovatebot.com/merge-confidence/) | |---|---|---|---| | [katex](https://katex.org) ([source](https://github.com/KaTeX/KaTeX)) | [`0.16.44` → `0.16.45`](https://renovatebot.com/diffs/npm/katex/0.16.44/0.16.45) | ![age](https://developer.mend.io/api/mc/badges/age/npm/katex/0.16.45?slim=true) | ![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/katex/0.16.44/0.16.45?slim=true) | --- ### Release Notes <details> <summary>KaTeX/KaTeX (katex)</summary> ### [`v0.16.45`](https://github.com/KaTeX/KaTeX/blob/HEAD/CHANGELOG.md#01645-2026-04-05) [Compare Source](KaTeX/KaTeX@v0.16.44...v0.16.45) ##### Bug Fixes - wrap vcenter mpadded in mrow for valid MathML ([#4193](KaTeX/KaTeX#4193)) ([ee66b78](KaTeX/KaTeX@ee66b78)), closes [#4078](KaTeX/KaTeX#4078) </details> --- ### Configuration 📅 **Schedule**: (UTC) - Branch creation - At any time (no schedule defined) - Automerge - At any time (no schedule defined) 🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied. ♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this PR and you won't be reminded about this update again. --- - [ ] If you want to rebase/retry this PR, check this box --- This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).  Co-authored-by: Renovate Bot <[email protected]> Co-committed-by: Renovate Bot <[email protected]>

greptile-apps bot reviewed Apr 5, 2026

View reviewed changes

grigoriy-reshetniak approved these changes Apr 5, 2026

View reviewed changes

Add test as suggested by Greptile

bafbae0

edemaine approved these changes Apr 5, 2026

View reviewed changes

Merge branch 'main' into main

3fafd5a

grigoriy-reshetniak merged commit ee66b78 into KaTeX:main Apr 5, 2026
9 checks passed

edemaine added the released label Apr 5, 2026

github-actions bot mentioned this pull request Apr 7, 2026

build(deps-dev): bump katex from 0.16.44 to 0.16.45 falgon/roki-web#1031

Merged

github-actions bot mentioned this pull request Apr 10, 2026

fix(deps): update dependency katex to v0.16.45 lacolaco/blog.lacolaco.net#1480

Merged

1 task

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

fix: wrap vcenter mpadded in mrow for valid MathML#4193

fix: wrap vcenter mpadded in mrow for valid MathML#4193
grigoriy-reshetniak merged 3 commits intoKaTeX:mainfrom
cyphercodes:main

cyphercodes commented Apr 5, 2026 •

edited by edemaine

Loading

Uh oh!

greptile-apps bot commented Apr 5, 2026

Uh oh!

greptile-apps bot Apr 5, 2026

Uh oh!

codecov bot commented Apr 5, 2026 •

edited

Loading

Uh oh!

edemaine left a comment

Uh oh!

Uh oh!

grigoriy-reshetniak commented Apr 5, 2026

Uh oh!

edemaine commented Apr 5, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Uh oh!

Conversation

cyphercodes commented Apr 5, 2026 • edited by edemaine Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Problem

Solution

Changes

Testing

Uh oh!

greptile-apps bot commented Apr 5, 2026

Greptile Summary

Confidence Score: 5/5

Important Files Changed

Flowchart

Uh oh!

greptile-apps bot Apr 5, 2026

Choose a reason for hiding this comment

Uh oh!

codecov bot commented Apr 5, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Codecov Report

Uh oh!

edemaine left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

grigoriy-reshetniak commented Apr 5, 2026

Uh oh!

edemaine commented Apr 5, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

cyphercodes commented Apr 5, 2026 •

edited by edemaine

Loading

codecov bot commented Apr 5, 2026 •

edited

Loading