Contains the OBJECT IDENTIFIER fragment that identifies the
instances of the base objects that need to be collected.
If cdcDGInstanceType is 'individual' then this value
should be the OID fragment that, when appended to each base
MIB object gives the fully instantiated OID to be fetched.
If cdcDGInstanceType is 'range' then this value
should be the OID fragment that, when appended to each base
MIB object gives the start of a range of object instances
that needs to be fetched.
If cdcDGInstanceType is 'subTree' then this value
should be the OID fragment that, when appended to each base
MIB gives the sub-tree under which all leaf object instances
need to be fetched.
This object's value may be modified at any time. The change
takes effect the next time data is fetched for this data
group.