As you can see from the open pics from the inside - there is a frame around the glass. I assume it is glued to the glass with something like rear view mirror glue.
It is just not visible from the outside.
The windows on my slides are normal framed windows which slide up to open for ventilation.
I'm a little concerned about the long term - five years or so - pliability of the seals. I'm also a little concerned about the way the 'frame' is attached to the glass. But if either of these becomes an issue with the concept of frameless windows - we will hear a lot about it.
Another concern is obviously that replacement of a broken window will be expensive - and might not be easy to find someone with the correct glass to make the repair.