Change #1201204 had a related patch set uploaded (by Physikerwelt; author: Physikerwelt):

[mediawiki/extensions/Math@master] WIP: MathJax4

https://gerrit.wikimedia.org/r/1201204

@FrederikHennecke1 do you have a test case for the a tag rewrite?

https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Math/+/1201204/2/modules/ext.math.mathjax.js

I get the impression that MathJax now supports links with a tags as well? If that were the case, we could entirely drop that workaround.

The current MathML looks like:

<math xmlns="http://www.w3.org/1998/Math/MathML" class="mwe-math-element mwe-math-element-inline">
    <mrow data-mjx-texclass="ORD">
        <mstyle displaystyle="true" scriptlevel="0">
            <mi>
                <a href="https://en.wikipedia.org/wiki/Energy" title="energy">E</a>
            </mi>
            <mo stretchy="false">=</mo>
            <mi>
                <a href="https://en.wikipedia.org/wiki/Mass" title="mass">m</a>
            </mi>
            <msup>
                <mi>
                    <a href="https://en.wikipedia.org/wiki/Speed_of_light" title="speed of light in vacuum"></a>
                </mi>
                <mrow data-mjx-texclass="ORD">
                    <mn>2</mn>
                </mrow>
            </msup>
        </mstyle>
    </mrow>
</math>

foreign-resources.cdx.json somehow seems to describe MathJax; however, I didn't find documentation on how this file was generated, or how it can be updated

See manageForeignResources.php and its make-cdx option.

In T409110#11345836, @Tgr wrote:

See manageForeignResources.php and its make-cdx option.

Thank you, that was easy.

I did a visual regression test and I noticed two issues:

First, the symbols for \Sampi and \Stigma were both changed. I am unsure if these changes are desired.

And the second, and probably more important, issue is that the symbol of \surd got moved down quite a bit.

Both these issues are in Firefox and Chrome.

I did a visual regression test and I noticed two issues:

That's cool. How did you do that?

First, the symbols for \Sampi and \Stigma were both changed. I am unsure if these changes are desired.

No

And the second, and probably more important, issue is that the symbol of \surd got moved down quite a bit.

The second sample also suffers from a very small 3 in \sqrt[3]x, which may be related.

https://tex.stackexchange.com/questions/694490/placement-of-surd-with-unicode-math-is-incorrect suggests a font-related issue

Adding

window.MathJax = {
	output: {
		font: 'mathjax-tex'
	},

seems to fix the surd baseline problem.

MathML (Firefox):

MathJax 4 with traditional tex font:

I found one problem with the new font:

I filed an upstream issue.

Change #1201204 merged by jenkins-bot:

[mediawiki/extensions/Math@master] Update MathJax to version 4.0.0

https://gerrit.wikimedia.org/r/1201204