Zoom on Touch devices, what exactly does it do?

Frankly, I don’t understand what is going on here.

1. Page zoom in the address bar is still 100%
2. If I use console.log to print width/height of window, screen or element they still have exactly the same values as they do at 100%, as if nothing is zoomed in at all.
3. But when I look at it, the screen is clearly zoomed in!
   What is going here? How do I even detect this? I just want to implement scroll while dragging an image through a zoomed in (via touch) zone. But there is no way to say it’s zoomed in!
   Also, calling window/scrollBy with constant dx/dy in this zoomed in (via touch) zone does nothing! It only works when my pointer is on the real boundary of the zone, which is not even accessible when zoomed in (via touch).