[winswitch] Question: How does Xpra communicate with X11-apps?

[Olbert, Nils]

Hello,

I am currently doing some research about alternatives to (plain) X11 and stumbled about this project.
I did some successful tests on my system and checked the wiki, anyways I was unable to find the answer to the following question:
I wonder if there is a technical overview of how Xpra works, especially how it interacts with X11-apps.
As far as I understand Xpra uses its own enhanced protocol, but how does Xpra communicate with a "dumb" X11-app which doesn't "speak" the xpra-protocol?
Does it use an internal Xvfb (or XDummy) to communicate with the applications or does an Xpra-host support both xpra-protocol and x11-protocol? Or is it completely different?

Thanks in advance