The real engine, in your browser: packages/core/src/mjsx.js running
against the same pure-js rasterizer the documentation screenshots are taken with.
Edit the code and it re-runs. Click and drag on the glass — that is a real touch
event going into UI.pointer.
Examples that need hardware — sensors, gpio, i2c,
camera, wifi — run here too, but a browser has none of those
natives, so each draws its own labelled fallback. That fallback is part of the example,
not a failure of the simulator.