v4-beta.4 crashing unexpectedly

[pkra]

Cf. Speech-Rule-Engine/speech-rule-engine#552

Using https://cdn.jsdelivr.net/npm/[email protected]/tex-mml-svg.js $\cdot \mathcal{O}_{\widetilde{X}}=\mathcal{L}\cdot \_{\widetilde{Z}}$ crashes -- it works fine in v4-beta.3.

In the browser, the error in the output reads a.childNodes[1] is undefined

[dpvc]

It turns out that this is due to the \_ and can be caused by that macro alone. It comes from the new code that attaches the original LaTeX to the MathML elements they produce, and in particular to the code that is handling superscripts and subscripts from _ and ^.

@zorkow, can you look into this? It is happening at

https://github.com/mathjax/MathJax-src/blob/818f68e044c7fdf55e08abdb7042985d6385bc24/ts/input/tex/TexParser.ts#L579

I think the solution is to wrap the entire section

https://github.com/mathjax/MathJax-src/blob/818f68e044c7fdf55e08abdb7042985d6385bc24/ts/input/tex/TexParser.ts#L561-L588

that handles _ and ^ in

if (!node.isToken) {
...
}

but since I'm not all that familiar with how the LaTeX processing is done, I'd like to hear your advice on it.