Other
Other requests and events in the core protocol exist. The first kind of requests is relative to the parent relationship between windows: a client can request to change the parent of a window, or can request information about the parenthood of windows. Other requests are relative to the selection, which is however mostly governed by other protocols. Other requests are about the input focus and the shape of the pointer. A client can also request the owner of a resource (window, pixmap, etc.) to be killed, which causes the server to terminate the connection with it. Finally, a client can send a no-operation request to the server.
Read more about this topic: X Window System Core Protocol