It was some time ago I looked into it, but wl_registry_listener registers a callback for when the compositor “declares” what protocol extensions it supports. This is painfully missing from X, but this makes Wayland much more modular/extensibly.

Wayland’s abstraction is basically a buffer. The client simply creates a buffer either in shared memory, or directly on the GPU and then passes the compositor a handle to the buffer. That’s it.

Also, it is sort of ingenious to compare the two — the XLib is a higher level lib than libwayland. There is absolutely no reason why someone could not create a wrapper for this — although I again ask, how often does one create an only X/only Wayland window without a framework.