Five things that used to be stubs. Each line is a live check; the canvas below must show a rounded box, a triangle and a heart-ish blob drawn entirely through Path2D.
Highlight some of this paragraph with the mouse. The moment you release the button, three lines above must report the exact text you highlighted and the node it starts in — no clicking needed. Then press the button below: it asks the same question one click later, which is where this engine differs from a browser (a press outside the selection clears it).
running...