You'll have seen code such as the following in the examples which is how MIBs are used:

$names = $snmpHost->useCisco_VTP()->vlanNames();

The call useXXX is a magic method in the SNMP class. It essentially instantiates a class as defined in XXX. So, for example:

• useSystem() instantiates \OSS_SNMP\MIBS\System
• useIface() instantiates \OSS_SNMP\MIBS\Iface
• useCisco() instantiates \OSS_SNMP\MIBS\Cisco
• useCisco_VTP() instantiates \OSS_SNMP\MIBS\Cisco\VTP
• useCisco_RSTP() instantiates \OSS_SNMP\MIBS\Cisco\RSTP

As you can see, underscores (multiple allowed) move further down the tree.

As part of instantiating the class, it also stores a reference to the SNMP object in the class (i.e. a reference to $snmpHost is stored in the object returned by useCisco_VTP()).

This instantiated class is returned where a method is then called. So:

$names = $snmpHost->useCisco_VTP()->vlanNames();

calls the vlanNames() function of the instantiated \OSS_SNMP\MIBS\Cisco\VTP class.