Perhaps you overlooked the following paragraph in the description I emailed out yesterday.
The parameter-tag and parameter-sequence may be omitted if the operation
has no parameters. The attribute-tag and attribute-sequence may be
omitted if the operation has no attributes or it may be replicated for
an operation that contains attributes for multiple objects. The data-tag
is present even when the data is omitted.
I believe that the mandatory data-tag makes it easier to decode because
with the mandatory tag, there is only a check of the tag in each cycle.
Without a mandatory data-tag, there would have to be a check for both
some end-of data index and the contents of the next tag.
> From cmanros at cp10.es.xerox.com Thu Jul 10 11:17:15 1997
> X-Sender: cmanros at garfield> X-Mailer: Windows Eudora Pro Version 3.0.1 (32)
> Date: Thu, 10 Jul 1997 09:53:25 PDT
> To: ipp at pwg.org> From: Carl-Uno Manros <cmanros at cp10.es.xerox.com>
> Subject: IPP> PRO - Comment on latest encoding proposal
> Mime-Version: 1.0
> Sender: ipp-owner at pwg.org> X-Lines: 30
>> From Bob's text:
>> 1.1 Syntax of Encoding
>> The encoding consists of:
>> . version
> . operation (for a request) or status (for a response)
> . parameter-tag
> . parameter-sequence
> . attribute-tag
> . attribute-sequence
> . data-tag
> . data (absent for some operations)
>> I thought that the discussion in yesterday's phone conference indicated
> that the attribute sequence could also be omitted. Also, do we require the
> attribute-tag and data-tag to always be present even if the
> attribute-sequence or data are empty?
>>> Carl-Uno Manros
> Principal Engineer - Advanced Printing Standards - Xerox Corporation
> 701 S. Aviation Blvd., El Segundo, CA, M/S: ESAE-231
> Phone +1-310-333 8273, Fax +1-310-333 5514
> Email: manros at cp10.es.xerox.com>