The Zend_Log class defines the following priorities:
<?php
EMERG = 0; // Emergency: system is unusable
ALERT = 1; // Alert: action must be taken immediately
CRIT = 2; // Critical: critical conditions
ERR = 3; // Error: error conditions
WARN = 4; // Warning: warning conditions
NOTICE = 5; // Notice: normal but significant condition
INFO = 6; // Informational: informational messages
DEBUG = 7; // Debug: debug messages
These priorities are always available, and a convenience method of the same name is available for each one.
The priorities are not arbitrary. They come from the BSD syslog protocol,
which is described in RFC-3164.
The names and corresponding priority numbers are also
compatible with another PHP logging system,
PEAR Log,
which perhaps promotes interoperability between it and Zend_Log.
Priority numbers descend in order of importance. EMERG (0)
is the most important priority. DEBUG (7) is the least
important priority of the built-in priorities. You may define priorities
of lower importance than DEBUG. When
selecting the priority for your log message, be aware of this priority
hierarchy and choose appropriately.