Some SNMP objects, like hrPrinterDetectedErrorState (http://tools.ietf.org/html/rfc2790#page-18) represent bitfields.

Zabbix triggers should be able to fire if certain bits are set.
Thus bitwise operators AND, OR, NOT, XOR left-shift and right-shift should be implemented in triggers.

http://www.zabbix.com/forum/showthread.php?t=11594 perfectly describes the problem.

Cheers,
--leo