[draft] Remove option mathjax_classes

[cpitclaudel]

The global approach in #395 isn't really sustainable: it requires all-ways cooperation between all projects that want to customize MathJax. Additionally, when processing a MyST document without Sphinx, the MathJax configuration changes are not performed (part of #347). And, of course, this approach of overriding the MathJax object causes issues down the line for projects that need to customize MathJax (the setting in Sphinx isn't sufficient, see sphinx-doc/sphinx#9450)

@chrisjsewell you wrote:

Its not really ideal that either package has to override the (global) configuration

I think the following two approaches would not require overriding the global config:

1. Add a custom script instead of touching the mathjax3_config variable; something like this, essentially:

   app.add_js_file(None, priority=0, body="""
      var MathJax = window.MathJax || MathJax;
      MathJax.options = MathJax.options || {};
      MathJax.options.processHtmlClass = (MathJax.options.processHtmlClass || "")
      + "|math";
   """)

2. Don't touch MathJax_config at all; instead, add an explicit mathjax_process class on all math nodes, either by changing docutils_renderer (this PR) or by adding a Docutils transform to processes all math nodes:

class ActivateMathJaxTransform(Transform):
    default_priority = 800

    @staticmethod
    def is_math(node):
        return isinstance(node, (math, math_block))

    def apply(self, **kwargs):
        for node in self.document.traverse(self.is_math):
            node.attributes.setdefault("classes", []).append("mathjax_process")

This PR isn't ready for merging; it's just to start a discussion.

[welcome]

Thanks for submitting your first pull request! You are awesome! 🤗

If you haven't done so already, check out EBP's Code of Conduct and our Contributing Guide, as this will greatly help the review process.

Welcome to the EBP community! 🎉

[chrisjsewell]

Don't touch MathJax_config at all; instead, add an explicit mathjax_process class on all math nodes, either by changing docutils_renderer (this PR)

Yeh but this would break any other extension that adds math and likely has not added explicitly the mathjax_process class. Therefore, I won;t be excepting this in its current form. Unfortunately docutils nor sphinx have really provided any good mechanism to deal with this

[cpitclaudel]

I don't understand — isn't it the reverse? What MyST currently does breaks extensions that use math.

[chrisjsewell]

No because the configuration sets mathjax to run on all elements with the math class, which is added for all math and math_blocks

[cpitclaudel]

Unless, of course, some other extensions modifies the Mathjax config (which is the issue at hand); and unless the document is processed with Docutils instead of Sphinx, too. That's why I was suggesting to add mathjax_process on relevant nodes. But it's probably OK to leave this unaddressed.