-When B<Instance> is set to B<true>, the value for requested OID is copied from
-plugin instance field of corresponding collectd value. If B<Data> block defines
-scalar data type B<Instance> has no effect and can be omitted.
+B<IndexKey> block contains all data needed for proper index build of snmp table.
+In case more than
+one table B<Data> block has B<IndexKey> block present then multiple key index is
+built. If B<Data> block defines scalar data type B<IndexKey> has no effect and can
+be omitted.
+
+=over 8
+
+=item B<Source> I<String>
+
+B<Source> can be set to one of the following values: "Hostname", "Plugin",
+"PluginInstance", "Type", "TypeInstance". This value indicates which field of
+corresponding collectd metric is taken as a SNMP table index.
+
+=item B<Regex> I<String>
+
+B<Regex> option can also be used to parse strings or numbers out of
+specific field. For example: type-instance field which is "vcpu1-cpu2" can be
+parsed into two numeric fields CPU = 2 and VCPU = 1 and can be later used
+as a table index.
+
+=item B<Group> I<Number>
+
+B<Group> number can be specified in case groups are used in regex.
+
+=back