Additional information to the manpage for english speaking users
(written by Patrick Kursawe <phosphan@gentoo.org>):

The XFree86 documentation (for 4.3 and later) contains the file
/usr/X11R6/lib/X11/doc/README.XKB-Config where you can find
information on how to use mutiple keyboard layouts.

Xxkb has no own configuration section where you can specify the keymaps -
just configure them for X and let xxkb switch between them.