Using SNMP V3 many device support the use of context parameter (see http://www.net-snmp.org/wiki/index.php/How_can_I_set_the_SNMPv3_context) in my case i need it for monitoring the new Brocade 85xx Class, they use "context" to create virtual fabric an example of use:
> snmpwalk -v 3 -u admin -c public "switchname" -n VF:128

The "VF:128" is used to retrieve the value from the switch context 128.
I see some path from the forum but is very old http://www.zabbix.com/forum/showthread.php?t=10399

Ask me for testing!