OP here– good point, that's not well explained in the article! And thanks to the others who have answered already, you're pretty much spot on. The core library

OP here– good point, that's not well explained in the article! And thanks to the others who have answered already, you're pretty much spot on. The core library, referenced here as `el`, contains a set of factory functions for describing various underlying processing nodes. So when you write `el.lowshelf()` you're just using one of the builtins (like how you might use a div, span, or button in a web app with React)