The number of jobs that are expected to complete before this
job is completed according to the implementation's queuing and
processing algorithm if no other jobs were to be submitted. In
other words, this value is the job's queue position. The agent
SHALL return a value of 0 for this object when there are no
other jobs that are expected to complete before this job.
A value of (-2) shall be used when the number of intervening
jobs is unknown.
NOTE the ISO DPA language does not include the case when
multiple jobs are in the 'processing' (or printing) state:
ISO DPA: Intervening-jobs
This attribute indicates the number of other jobs to be
processed before this job may be scheduled for processing. The
server shall set the value of this attribute to 0 when the job
begins processing.