{#if answer === 42} <p>what was the question?</p> {/if}
That is true... but of course, if you wanted 100% HTML, you aren't looking for a framework at all.
The approach in svelte is that you write the HTML parts of your app in HTML. It sounds almost silly to say -- that should almost be a silly circular statement -- but with some popular frameworks you write the HMTL for your app in something sorta like HTML but with various syntactic and semantic differences.
(You also write most of your UI logic in Javascript or typescript. The amount of syntax that is svelte-specific is pretty small, though semantically, the Javascript you write for the UI is built on the svelte concepts.)
That is, the closer to HTML the better.
Plain javascript is a crappy way to represent HTML because both the syntax and semantics are different (and sometimes there are conflicts, like with "class").
JSX is better than plain javascript because the syntax is closer, but the semantics are still Javascript, and there are still a number of differences you need to work through.
svelte is even better, because the HTML parts are strictly character-by-character the same as HTML, but you still need to know the syntax of a few escape mechanisms.
If there were a way to improve significantly on svelte then I'd be all for it. (Maybe HTMX? I'm skeptical of the approach of putting a network round-trip into every UI interaction, but they sure have nailed down the HTML aspect of it.)
Since all of this is client side (and display: none; is the best you can do in terms of not revealing everything to the user anyways) you don't even need any behavior language in HTML. Just set classes to elements and manipulate them with the framework from outside.
