Are the language/syntax differences documented somewhere? It's difficult to tell if something is an obscure early stage ecmascript proposal or a language feature specific to observablehq. For example in https://beta.observablehq.com/@mbostock/introduction-to-note...

  import {canvas as flood} with {height} from "@mbostock/randomized-flood-fill"

or how you define generators

  i = {
    let i = 0;
    while (true) {
      yield ++i;
    }
  }

etc