For example, the Catalyst switch includes one instance of the standard BRIDGE-MIB for each Virtual LAN in the switch. If the read-only community string is "public" and the read-write community string is "private", one could use "public@25" to read the BRIDGE-MIB for VLAN 25 and use "private@33" to read and write the BRIDGE-MIB for VLAN 33. If just "public" or "private" is used, the BRIDGE-MIB for VLAN 1 is accessed.
Also note that community string indexing does not affect access to MIBs which have only one instance. Thus "public@25" can be used to access RFC1213-MIB at the same time BRIDGE-MIB for VLAN 25 is being accessed.