Math is not rendered in HTML

[alexpearce]

Given the contents of foo.md:

The expression $$x = y$$ is boring.

When I run this command:

$ markup-toHTML foo.md

I get this output:

<p>The expression  is boring.</p>

The math has been removed.

I expect to get this:

<p>The expression $$x = y$$ is boring.</p>

Or perhaps this:

<p>The expression <math>x = y</math> is boring.</p>

(Preferably the former — keeping $$ — so that I can then pass the output to something like KaTeX.)

---

I get the same behaviour when using the API:

const { State } = require("markup-it");
const markdown = require("markup-it/lib/markdown");
const html = require("markup-it/lib/html");

const text = "The expression $$x = y$$ is boring.";

const mdState = State.create(markdown);
const document = mdState.deserializeToDocument(text);
const htmlState = State.create(html);
// console prints "<p>The expression  is boring.</p>"
console.log(htmlState.serializeDocument(document));

I've tried following through the logic of the conversion, but I haven't found anything obvious. My only clue is that the math element is represented as a node with isVoid: true. It might be that void nodes aren't converted to HTML, but I haven't found the line that would drop such nodes.