What is the server-client relationship between a terminal emulator, a window manager and a X server processes?

1. In APUE (see the figure below), how do a terminal emulator process and a window manager (e.g. openbox) process communicate? Is a temrinal emulator process a client of a window manager process, based on Unix domain socket? 2. What is the relation of X server process to a terminal emulator process and a window manager process? Specifically: xlsclients output contains lxterminal. Does that means that a terminal emulator process is a client of X server? $ xlsclients -a | grep -i lxterminal ocean lxterminal xlsclients output doesn't contain a window manager process. Does that means that a window manager process is not a client of X server? $ xlsclients -a | grep -i openbox $