As siblings have commented, it's not clear what reaction is obscured by your lack of words; but, if it's a veiled comment on the inadvisability of doing this, the author beat you to it:
> Warning: All of this doesn’t really follow any best practices for working with html, css or javascript - on the contrary: what we will be doing may look horrible to some people, and rightfully so - so you may not want to try those things at work just yet.
I do - that's great fun. I'm actually a bit surprised that the browser bothers to add text nodes to the DOM tree as normally there wouldn't be any reason to, but it's great to learn that they do, and might be something I'll have a play with one day.