[IPP] Please explain the use of "preferred" attributes

[IPP] Please explain the use of "preferred" attributes

[IPP] Please explain the use of "preferred" attributes

Petrie, Glen glen.petrie at eitc.epson.com
Tue Nov 1 22:50:54 UTC 2011

Thanks for explanation, it helps.  Unless, I missed it, there should a
similar explanation in the specification; so that people writing clients
will understand the rational when using the preferred capability.



In your first statement, you state that the "printer could" versus the
"printer will"; therefore, I assume the ""use"" of "preferred" is
optional and that the client could return an invalid job for your
example.    So, is the User in control of whether they want a printer to
use "preferred" value.  I assume the Print Client could respond to
difference in the sent and returned job ticket in various ways (and
mostly likely should).  Can the Print Client tell the printer not to use
preferred values even if the printer supports preferred values?






From: Michael Sweet [mailto:msweet at apple.com] 
Sent: Tuesday, November 01, 2011 2:38 PM
To: Petrie, Glen
Cc: ipp at pwg.org
Subject: Re: [IPP] Please explain the use of "preferred" attributes




The semantic definition is that the Printer may return substituted
values for unsupported attributes in a Create-Job, Print-Job, Print-URI,
or Validate-Job response. That is, if you specify duplex printing on
transparency media, the printer could return sides-preferred with
"one-sided" or media-col-preferred with a media-type other than
transparency to tell the client that it will print the job differently
than requested.


In the case of attributes like "copies", a printer may normally support
up to (for example) 999 copies for uncollated output, but may only
support 99 copies for collated output.  Or the printer may not be able
to support copies for a given document or document format.


In short, previously all the client has known is that particular
attributes or values were not supported (or conflicted), but not what
attributes would be used by the printer instead (typically the default



On Nov 1, 2011, at 12:37 PM, Petrie, Glen wrote:

Discussion on wd-ippjobprinterext3v10-20111013


In Section 6.4 I don't understand the idea of "... the Printer would
prefer to use".  Does this the Printer will override Job Ticket values?
While, the printer has limitation or constraints which are reported in
the capability information; what does it mean when the printer has
"copies-preferred" (section 5.3.2) - does this mean the User wants 3
copies but the Printer prefers to only print 2 !!!  Very Strange.
There could be a concept of "recommended" attributes that would apply to
a very small set of attributes (copies is not one of them) and would be
presented to the User in such a way as to identify it as "recommended".

*      The same comment applies to almost all the other "preferred"





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