ignoreHtmlClass not checked for MathML content

Issue Summary

The ignoreHtmlClass option seems to have no effect on MathML rendering. Maybe it is intended behaviour – I couldn't tell from the documentation.

Steps to Reproduce:

1. Configure

window.MathJax = {
  options: {
    ignoreHtmlClass: 'nomathjax',
  },
};

2. Run it on

<math><mi>x</mi></math>
<math class="nomathjax"><mi>x</mi></math>

3. Both <math> tags are processed by MathJax

There are situations where I'd like MathJax to render most of the MathML content, but occasionally allow the browser use its native MathML renderer (because e.g. of images embedded in <mtext>). I thought ignoreHtmlClass would help here.

Technical details:

• MathJax Version: 3.2.0