X11::Protocol is a client-side interface to the X11 Protocol (see X(1) for
information about X11), allowing perl programs to display windows and
graphics on X11 servers.

A full description of the protocol is beyond the scope of this
documentation; for complete information, see the _X Window System Protocol,
X Version 11_, available as Postscript or *roff source from
'ftp://ftp.x.org', or _Volume 0: X Protocol Reference Manual_ of O'Reilly &
Associates's series of books about X (ISBN 1-56592-083-X,
'http://www.oreilly.com'), which contains most of the same information.