SvelteJS under the hood

SvelteJS is a modern compiled JS framework that made a lot of noise in 2019 and became the most interesting framework according to "State of JS", and is becoming very popular. At the same time around him developed a lot of controversy and contradictions, misreadings and just rumors.

Is that a radically new approach? Is SvelteJS a framework or it's just a compiler? Does it disappear, and where is the "magic"? How does it work, and what does the "cybernetic improvement" of web applications have to do with it?

Let's look under the hood of this interesting framework and try to figure it out!