The xcb-util module provides a number of libraries which sit on top of
libxcb, the core X protocol library, and some of the extension
libraries. These experimental libraries provide convenience functions
and interfaces which make the raw X protocol more usable. Some of the
libraries also provide client-side code which is not strictly part of
the X protocol but which have traditionally been provided by Xlib.

These libraries are currently included, roughly ordered by maturity:

aux: Convenient access to connection setup and some core requests.
atom: Standard core X atom constants and atom caching.
property: Callback X property-change handling.
event: Callback X event handling.

WWW: https://xcb.freedesktop.org/