> The point is that all code starts as simple text, and is parsed and compiled into some lower layer

Yup

> What actually does the compilation is irrelevant.

Nope. It is relevant. For the stuff you put between script tags there's at the very least https://github.com/tc39/ecma262 that you can look at and tell exactly what's going on with your code.

With Vue (and, yes, React and Svelte and Angular): who knows? It might very well evalueate strings at runtime for all we know.

> All of these JS frameworks (React+JSX, Vue+HTML, Angular, Svelte, etc) require template compilation into an actual JS render function before a browser ever runs it,

Yup. It's an additional, different step before it can even get to the browser. The problem with this step is that for most of this code there's not even a coherent specification of what it is, and how it's compiled.

> and Vue's documentation already describes exactly what you can run

It really doesn't. For example, here's the "documentation" on v-for:

    Expects: Array | Object | number | string | Iterable

Expects where? Is this correct:

    <div v-for="{ a: 1, b: 2 }"></div>

Answer: no. Because the actual description of what is expected is written in examples. Same goes for every single other directive. I mean, v-bind expects "any (with argument)" (what does this even mean?) and v-if expects "any", and both of these are false statements.