ISO DPA: Number-of-documents
This attribute indicates the number of documents in the job.
The number indicates how many Print operations that specified a
document (of any document-type have been submitted for
printing until job submission has been completed; at that point
this attribute shall then indicate the total number of
printable documents, fonts, and resource objects submitted by
the client in the job. If the first Print operation does not
contain a first-document component (see 8.2.1), the value of
this attribute shall be 0.
The server shall count fonts and resource objects passed to the
server by means of Print operation invocations, as documents
for the purposes of this attribute.