Re: CFD: eXIf 2017-05-31

03.06.2017 14:07, Glenn Randers-Pehrson пишет:
> We have the following already in the PNG specification version 1.2.  I suppose
> we could copy it into the png extensions document, where the eXIf chunk
> specification will reside if we approve it:
>
> <p>The words "must", "required", "should", "recommended", "may", and
> "optional" in this document are to be interpreted as described in
> RFC-2119, which is consistent with their plain English meanings.  The word
> "can" carries the same force as "may".
Well, I think this would be nice, especially as the most final (W3C/ISO) 
version of main PNG specification miss these words.

But why not to add this reference to proposal too? In practical terms 
that doesn't produce very much difference, but on formal side single 
addition will looks like word "recommended" is interpreted by readers 
will in proposal and magically transforms to rfc2119 in extension 
specification.

It might be influence of my (bureaucratic) work, but I wish to prevent 
any possible misinterpretation and inconsistency. When I read EXIF 
specification I had strong feeling that authors supposed that thumbnail 
would be updated with image every time. But there is no explicit 
declarations of it and so we experience issues we discuss before.

And there is at least one inconsistency in this paragraph for now:
If recommendation about "data should be considered to be of historical 
value only" is strong condition, not weak one, then it is pretty clear 
set priority of PNG chunks over EXIF data. So sentence "It is beyond the 
scope of this specification to resolve potential conflicts between data 
in the eXIf chunk and in other PNG chunks." may be valid only in case of 
independent knowledge of the validity of both EXIF data and PNG chunks.
I think addition of reference to this exact case (and change order of 
sentences) will make specification more clear. Or it is possible to just 
strike out this sentence.
It's not easy to inspect my own thoughts, but it's possible that 
sentence about "beyond the scope" was reason I treat recommendation 
about "historical" as a weak condition.

-- 
Have a nice DOS.

Pavel Zlatovratskii [email protected]; [email protected]


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