@bramus Some random thoughts:

- Making the `<style>` contentEditable in this example is fun :)
- I wonder if it is worth it to simplify registering the tokens: when we iterate through them, we already know their types, so we could potentially register any new types as they go (though, I imagine, this might be slightly less performant with extra checks; but less code, and no need to maintain the list of the tokens to highlight).