Displaystyle="true" does not apply to all elements within an mrow

[samimaattaCelia]

Issue Summary

When mrow is given the attribute displaystyle="true" it should apply to all elements within said mrow. This does not happen with MathJax.

Both of the summation expressions are nested inside an mrow element with the attribute displaystyle="true". Visually both of them should appear as uppercase symbols (as if they were block equations), where the numbers 5 and 6 should be under them, not as subscripts.

MathJax 4 output:

Firefox's native output:

OS: Windows 11
Browser: Mozilla Firefox 153.0

Steps to Reproduce:

Use the code to render:

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <mrow displaystyle="true">
  <munder>
    <mo>∑</mo>
    <mn>5</mn>
  </munder>
  <munder>
    <mo>∑</mo>
    <mn>6</mn>
  </munder>
  </mrow>
</math>

Technical details:

• MathJax Version: 4
• OS: Windows 11
• Browser: Mozilla Firefox 153.0

I am using the default MathJax configuration and loading MathJax via

<script src="https://cdn.jsdelivr.net/npm/mathjax@4/tex-mml-chtml.js" defer></script>

[dpvc]

MathJax's MathML support is based on MathML3, the current official version of MathML from the W3C. MathML4 is currently a working draft, and MathML-Core is a candidate recommendation. MathML-Core is a more restricted version of MathML4 that limits the elements and attributes available, making it easier to implement in browsers, thus most browsers implement MathML-Core. Firefox has a more complete implementation of MathML3 with MathML-Core added on top (or perhaps it is actually MathML4; I'm not involved with that, so I don't kn owe the details for certain).

In MathML3, the displaystyle attribute is only allowed on the math, mstyle and 'mtable' elements; MathML4 and MathML-Core extend that to all elements. Similarly, scriptlevel is only allowed on math and mstyle elements in MathML3, but on all elements in MathML4 and MathML-Core.

One work-around would be to change the mrow with the displaystyle to an mstyle element instead. This could be done via an mmlFilter on the MathML input jax. Here is a configuration that does that:

MathJax = {
  mml: {
    mmlFilters: [
      ({data: mml, document}) => {
        const adaptor = document.adaptor;
        const nodes = Array.from(mml.querySelectorAll('[displaystyle]:not(mstyle,math,mtable)'));
        for (const node of nodes) {
          const mstyle = adaptor.node('mstyle', {displaystyle: adaptor.getAttribute(node, 'displaystyle')});
          adaptor.removeAttribute(node, 'displaystyle');
          adaptor.replace(mstyle, node);
          adaptor.append(mstyle, node);
        }
      }
    ],
  },
};

this filter looks for displaystyle attributes on nodes other than mstyle, math, or mtable, removes the attribute and wraps the node in an mstyle with the corresponding displaystyle attribute. I think that should do what you are asking for.

[samimaattaCelia]

Thanks again for the answer! I should have maybe specified that I'm introducing these features/bugs, since MathJax is used in a number of ebook reading systems. Seems like I will try to reach out to those developers and see how they respond. (This particular item is not the most pressing, but great that you took the time to flesh out how to do it.)