X11 window managers historically have a notion of screens - each screen has a distinct set of windows and you can switch between them using the same physical display.
I'm recording a screencast so I would really like to have a secondary, smaller X11 screen on which a handful of windows will be displayed, while keeping the content of my main screen intact and hidden. So I would like to have a virtual screen in a window, which will contain other windows. Then I can simply grab this window for my screencast. How do I do that?
I would prefer a native X11 approach (maybe there are window managers which do that with ease?)
Maybe there's a way I can declare a virtual monitor for X11 server to use, that ends up displayed as a window?
Failing that, I guess I could use Xvfb or VNC, but obviously it is harder to set up. Maybe some other popular approaches are there?