[dyingkneepad]

The X11 protocol is highly documented. There are many decent books about it. The Xlib and XCB are small wrappers around the protocol. Once you learn one, jumping to the protocol bits is easy.

Wayland is also a protocol and also documented, somewhere. I heard it has support for extensions and they are also in some repo. Search: https://cgit.freedesktop.org/

A big difference between the Wayland and X11 protocols is that X11 covers a lot more things, like drawing. Also, X11 has the concept of a client that is also a compositor and tons of interfaces for clients and compositors and the Xserver to interact. Wayland has none of those things, because the entity that implements the protocol is the compositor, unlike X.

Everything that's not covered by the Wayland protocol or extensions has to be defined/implemented by the Compositor, and that's where Fragmentation is killing us. Each compositor is allowed to implement whatever it wants to deal with those things. I am not aware of any standards here, although I would recommend trying to look if any XDG standards exist for those.