Sorry I didn't look Sten at the source code in Chrome however I am doing an online course at the moment in integrating SVG + HTML 5 and I am also having to use and learn Java script as well. As things progress I am thinking I am now too old to learn a new code language but I am OK with HTML 5 it is easier to learn. Nice example that you have used, I take it from my own experience that Java script was also used here for the zoom.