Syslog messages--as standardized in RFC3164--embed a priority number
(the PRI part) which is composed of a severity and a facility
value. The constants which encode these values are specified in
section 4.1.1, and are made available by this module. For instance,
the exportable LOG_FTP constant has a value of 11, the value for the
FTP facility.

WWW: http://search.cpan.org/dist/Log-Syslog-Constants/