What's in the Wayland package
When you install "wayland" in your Linux distribution, you'll most likely end up with the freedesktop.org distribution of libwayland-client, libwayland-server, wayland-scanner, and wayland.xml. Respectively, these will probably be in /usr/lib & /usr/include, /usr/bin, and /usr/share/wayland/. This package represents the most popular implementation of the Wayland protocol, but it is not the only one. Chapter 3 covers this implementation of Wayland in detail; the rest of the book is equally applicable to any implementation.
wayland.xml
Wayland protocols are defined by XML files. If you locate and open "wayland.xml" in your favorite text editor, you will find the XML specification for the "core" Wayland protocol. This is a high-level protocol — built on top of the wire protocol that we'll discuss in the next chapter. Most of this book is devoted to explaining this file.
wayland-scanner
The "wayland-scanner" tool is used to process these XML files and generate code from them. The most common implementation is the one you're examining now, and it can be used to generate C headers & glue code from XML files like wayland.xml. Other scanners exist for other programming languages, notably wayland-rs (Rust), waymonad-scanner (Haskell), and more.
libwayland
The two libraries, libwayland-client and libwayland-server, include an
implementation of the wire protocol for each end of the connection. Some common
utilities are offered for working with Wayland data structures, a simple event
loop, and so on. Additionally, these libraries contain a pre-compiled copy of
the core Wayland protocol as generated by wayland-scanner.