Top to bottom is dependency order. A concept sits as far down as its longest chain of prerequisites pushes it, so every line points downhill.
Beginner. Foundations. Each is reachable on day one with nothing but the lesson in front of you.
Advanced. Each rests on several beginner concepts at once.
Expert. Abstract structures and open questions, built on many advanced ideas at once.
Colour is the area of the language, not difficulty. The edges are the ones that cross between areas — a collection earning you objects, a builtin earning you statistics. Hover to light a chain; click for a concept's own roadmap.
