Currently, "printer-uri" is a MANDATORY Operation Attribute of the
Create-Job operation (see section 15.3.4.3 Validate the presence of a single
occurrence of required Operation attributes).
[Paul Moore] My reading of this was that it was a 'virtual'
attribute. You were not expected to encode it in the IPP packet. This is the
same way that the creatjob request does not encode the user name (it can
choose to do) rather the user is inferred from the transport.