Forerunnerz wrote:

I tried src.overlays.layer++ but it says undefined var.

overlays is as you should know a list, so it makes sense for it not to have non-list, atom vars, don'tcha think? :P

What's the correct var for this?

There is none. While you can read the overlays list's elements, they are stored in a special internal format, as the DM Reference says, which cannot be modified. Therefore, to change something about an overlay, you must replace it with a new one.