I'd really love a deep dive on what reference types enable and what limitations they have. Why are reference types not an end-all be-all "When is WebAssembly Going to Get DOM Support?" 'we have them now' answer?

I think the easiest way to explain reference types is to contrast it with how we used to do it.

WASM strings aren't JS strings; they're byte arrays. (WASM only knows about bytes, numbers (integers/floats), arrays, functions, and modules.)

In the old days, to pass a JS string to WASM, you'd first have to serialize the JS string to a byte array (with the JS TextEncoder API, usually), and then copy the byte array into WASM, byte by byte. That took two O(n) steps, one to serialize to a byte array, and another to copy the byte array.

Well, now, you can serialize the JS string to a byte array and then transmit it by reference to WASM, saving you a copy step. You still have one O(n) step to serialize the string to a byte array, but at least you only have to do it once, amirite?

If you want your WASM to call `document.createElement("div")`, you can pass `document` and `createElement` by reference from JS to WASM, then have WASM create an array `['d', 'i', 'v']`, and send all of those back to JS, where the JS will convert the array back into a JS string and then call `createElement.call(document, "div")`.

It's better, certainly, but it's never going to be as fast as just calling `document.createElement("div")` in JS, not as long as `createElement` requires a JS string instead of a byte array.

The proper fix would be to define a whole new "low-level DOM API", which would work exclusively with byte arrays.

That's what we're probably never going to get, because it would require all of the browser vendors (Apple, Google, Microsoft, and Mozilla) to standardize on a new thing, in the hopes that it was fast enough to be worth their trouble.

Today, they don't even want to discuss it; they think their time is better spent making existing web apps faster than making a new thing from scratch that ought to be faster, if only a multi-year (decade??) effort comes to fruition.