W3C home > Mailing lists > Public > public-html@w3.org > February 2009

RE: Example canvas element use - accessibility concerns

From: John Foliot - WATS.ca <foliot@wats.ca>
Date: Sat, 21 Feb 2009 11:22:52 -0800
To: "'Ian Hickson'" <ian@hixie.ch>
Cc: "'HTML WG'" <public-html@w3.org>, "'W3C WAI-XTECH'" <wai-xtech@w3.org>
Message-ID: <077601c99459$cabfafd0$603f0f70$@ca>
Ian Hickson wrote:
> 
> 
> If the image is actually a _replacement_ for text that otherwise
> existed,
> why would the user care that the author had made the stylistic choice
> to use an image instead? I don't understand.
> 
> Specifically, the example in the spec is talking about an author who
> has something like this:
> 
>   <p>In the common case, the data handled by the tokenization stage
>   comes from the network, but it can also come from script.</p>
>   <p>The network passes data to the Tokeniser stage, which
>   passes data to the Tree Construction stage. From there, data goes
>   to both the DOM and to Script Execution. Script Execution is
>   linked to the DOM, and, using document.write(), passes data to
>   the Tokeniser.</p>
> 
> ...and decides to replace the text with an image. Why should there be
> _any_ difference for the non-visual user? What the spec proposes:
> 
>   <p>In the common case, the data handled by the tokenization stage
>   comes from the network, but it can also come from script.</p>
>   <p><img src="images/parsing-model-overview.png" alt="The network
>   passes data to the Tokeniser stage, which passes data to the Tree
>   Construction stage. From there, data goes to both the DOM and to
>   Script Execution. Script Execution is linked to the DOM, and, using
>   document.write(), passes data to the Tokeniser."></p>
> 
> ...seems like exactly what the user would want. Why should the user who
> doesn't have access to images be affected here?

OK, fair questions.  The problem however is that you are making a judgment
call of what the 'user' might want based upon your subjective point of view,
which is based upon your subjective interpretation of the author's intent.
How do you know these things? You yourself are not a blind user, so how do
you know what any blind user might want, never-mind all blind users?  I do
not ask this out of malice, but simply to open up the question - how do you
know? 

Thing is, the author didn't provide text, he provided an illustration
(parsing-model-overview.png).  Surely you cannot be suggesting that he
opened up a graphics program and used it to make an image simply so that he
could use a display font?  This is 2009, and that is simply a strawman I
find hard to accept today. (Besides, what about web fonts?)  So the image
then is more likely a flow chart, or a Venn diagram or something similar to
that - and that is legitimate, but introduces an aspect beyond simple text
representation as it is a more complex visualization.

There is a world of difference between the two examples you pose above.

So, to solve the 'problem', I would likely go with:

   <p>In the common case, the data handled by the tokenization stage
   comes from the network, but it can also come from script.</p>
   <img src="images/parsing-model-overview.png" alt="flow chart illustrating
the parsing model overview" longdesc="parsing_model_overview.html">
   <p>The network passes data to the Tokeniser stage, which
   passes data to the Tree Construction stage. From there, data goes
   to both the DOM and to Script Execution. Script Execution is
   linked to the DOM, and, using document.write(), passes data to
   the Tokeniser.</p>

(* where parsing_model_overview.html would also attempt to explain the
visualization in greater detail than the subsequent on-screen text provides)

The education piece of the spec (and I grant that you have spent time
working on that, and that is a good thing) needs to also point out that
images are not the appropriate place to be putting large blocks of critical
text - something that WAI has been saying for close to a decade. 

***

At the start, I asked you "how do you know" what a blind user needs or
wants?  Thus it would be fair to ask "how does JF know?"  Honest answer - I
don't.  I don't know what every blind user might want, as, after working
with many, many blind users over the past decade I've learned that they are
not blind people, they are people who are blind, and every person is
different.  But I do know this:

Our best understanding at this time is that the majority of daily users of
screen reading technology generally prefer terse descriptions of images on
first pass, but we all (should) understand that there are times when a more
detailed description of the image is appropriate or warranted - and so the
spec should allow for that possibility too (@longdesc and/or ARIA
labeledby).  For the sighted readers out there, surely you can understand
the difference between glancing at an image, versus truly studying an image,
and so we need to provide that kind of potential experience to the
non-sighted user as well.  Presuming that all non-sighted users will always
want the fully detailed explanation is paternalistic and condescending - it
presumes that all non-sighted users are a monolithic group that act and
interact with the web identically, which we all must know to be not true (I
certainly do).

What experience and the little research we do have does suggest then, is
that, while well-meaning, the current example as suggested is likely not
appropriate or appreciated.

Cheers!

JF
Received on Saturday, 21 February 2009 19:23:30 UTC

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