Math input error when mixing MathML and a HTML hyperlink

Issue Summary

MathJax 4 produces a math input error when rendering a MathML equation that also has other HTML elements in it.

OS: Windows 11
Browser: Mozilla Firefox 153.0

Expected output (using Firefox's native rendering):

Steps to Reproduce:

Render the MathML equation in question:

<math xmlns="http://www.w3.org/1998/Math/MathML">
        <mo>|</mo>
        <mi>x</mi>
        <mo>+</mo>
        <mi>y</mi>
        <mo>|</mo>
        <mo>&lt;</mo>
        <mo>|</mo>
        <mi>x</mi>
        <mo>|</mo>
        <mo>+</mo>
        <mo>|</mo>
        <mi>y</mi>
        <mo>|</mo>
        <mtext>
        <sup>
            <a href="https://en.wikipedia.org/wiki/Triangle_inequality">Triangle inequality (Wikipedia)</a>
        </sup>
        </mtext>
      </math>

It is a bug, since it should be possible to have HTML markup inside MathML markup as per MathML Core 2.2.1 HTML and SVG.

Technical details:

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

I am using the following the default MathJax configuration.

Loading MathJax via:

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

Start by running the provided MathML example with MathJax 4's default tex-mml-chtml.js configuration in Firefox, then trace the math input error triggered by the HTML hyperlink inside mtext. Done means the equation renders without an input error while retaining the hyperlink.