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Re: 'Non-economic' rationale for backward compatibility

From: Loretta Guarino Reid <lguarino@adobe.com>
Date: Wed, 20 Mar 2002 10:07:53 -0800
Message-Id: <200203201807.KAA14852@patagonia>
To: gian@stanleymilford.com.au
cc: w3c-wai-gl@w3.org
   Our discussion of PDF is mixing issues and problems with PDF as a 
representation format and Acrobat Reader as a user agent. Since Acrobat Reader 
is the most common user agent for PDF files, this is understandable. It 
certainly highlights the relationship between content and user agent that 
makes the two sets of guidelines so interdependent.
> In terms of Acrobat files however, even Acrobat 5.0 suffers from a
> certain lack of manipulability (for want of a better word).  It is not
> possible to, say for example, turn all the images off (which would
> decrease download time)

I agree that it would be a valuable enhancement to the Acrobat user agent to 
provide a way to turn all the images off. In a Tagged PDF file, there is even 
alternate text that could be provided for the images. Because of the way the 
PDF format is defined, however, this would not decrease download time. There 
are advantages and disadvantages to have a "complete container".

> Also this brings us back to the problem of file download and sizes -
> instead of opening a page, the user is required to download information
> which may be many hundreds of pages long. This poses a problem for
> people using modems (any kind of modem) instead of broadband (and even
> for people using broadband if it is a particularly large file). It
> causes problems for regional users (and their electric fences for those
> OzeWAI attendees).  It costs more to the user.

I agree that smaller files are faster than larger files. For a properly 
linearized PDF file, it is not necessary to download the entire file to start 
displaying it. Browsers with byte-server support will download data as it is 
needed. Now we are getting deep into user agent requirements...

> And in order for people to access these PDF files they need the latest
> version of Jaws. As Jaws retails at several thousand dollars (depending
> on which currency), this isn't something that people will do every year.

The question of how quickly assistive technology will support different 
formats is a real issue for any new technology. Almost by definition, any new 
functionality will only be available in recent releases. I think this is at 
the heart of the tension between our backwards compatability needs and our 
desire to use new technologies, like SVG, that were designed with an eye 
towards accessibility and provide some good solutions to problems that are 
difficult to solve in other technologies.

As an aside, there are screen readers that aren't quite as expensive as JAWS 
that support PDF. But still only in their most recent releases. And still not 
free, of course.
> And to Cynthia's analogy- yes we require that people have their own
> assistive technology, whether it be a wheelchair or a screen-reader. But=
> we don't make a ramp that only motorised wheelchairs can climb, and tell=
> the people who use their wheelchairs manually to come back when they
> have some more money.
> Gian
Received on Wednesday, 20 March 2002 13:08:33 UTC

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