W3C home > Mailing lists > Public > public-html@w3.org > April 2011

Re: example spec text for longdesc

From: Laura Carlson <laura.lee.carlson@gmail.com>
Date: Thu, 7 Apr 2011 12:59:52 -0500
Message-ID: <BANLkTikRYDnV+hyVjLNubSx0XOB-3-ECzQ@mail.gmail.com>
To: Steve Faulkner <faulkner.steve@gmail.com>
Cc: HTML WG <public-html@w3.org>, Jonas Sicking <jonas@sicking.cc>, Maciej Stachowiak <mjs@apple.com>, Charles McCathieNevile <chaals@opera.com>, Aryeh Gregor <Simetrical+w3c@gmail.com>, "Edward O'Connor" <hober0@gmail.com>
Hi Steve and everyone,

Thanks for your email, Steve.

> The use case for a description I encounter most often in web applications is
> data presented in an image, I consider that having access to both image and
> a structured HTML representation would be useful for a range of users
> inlcuding users of screen magnifiers AT which traditonally do not process
> HTML or provide access to content other than that provided by the browser.

I agree. It should be a person's option and choice to obtain access to
long descriptions of data visualizations in a device independent
manner. They should be available to anyone who would like to opt into
having them.

Something to keep in mind is that, 1.) data visualizations and  2.)
long descriptions of data visualizations have the same aim but have
typically served different audiences.

1.) The aim of data visualizations (charts and graphs) has typically
been to make data easier to understand to sighted people rather than
simply providing raw data in a table.

2.) The aim of long descriptions of data visualizations has typically
been to make the data easier to understand to people with disabilities
rather than simply providing raw data in a table.

Notice both aims are to *understand data*. Providing the data itself
with either number one or number 2 is a nice touch but it is not the
primary aim of either.

Joe Clark talked about this a few years ago in a WCAG comment. He said,
"To use an analogy over again, diagrams and data are like a suitcase
that can be unpacked but not easily repacked. If data were
understandable by themselves, we wouldn't make a chart. I can assure
the Working Group that giving nondisabled people a really nice chart
and disabled people a table with 10,000 or more data points does not
constitute equality in any sense."

WCAG revised their example after his comment to read: "A bar chart
compares how many widgets were sold in June, July, and August. The
short label says, 'Figure one - Sales in June, July and August.' The
longer description identifies the type of chart, provides a high-level
summary of the data, trends and implications comparable to those
available from the chart. Where possible and practical, the actual
data is provided in a table."

> I also think in cases such as the thematic images example:
> http://dev.w3.org/html5/alt-techniques/#images-enhance
> where a link is provided to further information about the image:
> http://www.tate.org.uk/servlet/ViewWork?cgroupid=-1&workid=15984&searchid=false&roomid=false&tabview=text&texttype=10
> would be useful to a range of users.

I agree. From my perspective a link serves this purpose, as it is not
redundant information. Like data tables of charts and graphs, it is
further information useful to all.

Maybe this is where the differences exist, Steve. In my research what
I have gathered is that the target of a longdesc is generally or
should be *redundant information* to most sighted users.

Steve, do you consider the target of a longdesc attribute to be
*additional information* or *generic information* or *ancillary
information* or *detailed information* for everyone?

Maybe we need to agree on a common definition of the target of a
longdesc. Let's get back to basics.

HTML4 said:
* "This attribute specifies a link to a long description of the image.
This description should supplement the short description provided
using the alt attribute."
* "longdesc "link to long description (complements alt)."
* "The longdesc attribute allows authors to make frame documents more
accessible to people using non-visual user agents."

What would be your ideal definition the target of a longdesc? To you
what is its purpose, Steve? Everyone else please feel free to jump in

>>Again it is akin to closed captions being redundant to most people who
>>can hear
> in this case a device independent  method to access closed captions is
> usually provided even though it is not considered useful for users who do
> not have a hearing impairment or those who cannot see the captions.


> I would
> not encourage authors to not provide device independent access to
> closed captions.

I wouldn't either. I mention "a device independent mechanism." in the
example spec text:

"User agents should allow users to follow such description links. To
obtain the corresponding description link, the value of the attribute
must be resolved relative to the element. User agents should provide
the user an option or preference to access the content via a device
independent mechanism. For specific details consult the User Agent
Accessibility Guidelines (UAAG 2.0) and its implementation documents.
Since an img element may be within the content of an a element, the
user agent's mechanism in the user interface for accessing the
"longdesc" resource of the former must be different than the mechanism
for accessing the href resource of the latter."

How could that be made clearer?

>>Another analogy would be if we were to make alt visible by default or
>>provided visible indicators of  alt by default. Making indicators
>>visible by default would cause needless work for designers to hide
>>them or frustration to sighted users if designers didn't hide them.
> alt is a different case as its display is contingent, its also almost
> ubiquitous, every image on every page should have an alt attribute, the vast
> majority of images do not require a description.

This is true. But as Leif pointed out earlier, legacy longdesc targets
exist which are bogus.

ALL of those would display if an on screen indicator was set to "on" by default.

>>Many artists, designers, and marketers do not want
>>their visual designs changed/ruined with visible link text or
>>indicators. Being  free from a visual encumbrance is an asset.
> a simple CSS decalaration (example only this does not work):
> img[longdesc]::marker {display:none}
> will hardly be a barrier  to any of the above.

The same would be true of:

img[longdesc]::marker {display:inline}

This brings to mind skip navigation links. The majority of sites that
provide skip navigation links do not make them visible by default.
They hide them from the sighted users. It causes extra work for
designers to hide them.

It would be good to get browser vendors input on this point.

So what do browser vendor think?  Jonas, Maciej, Chaals, Aryeh,
Edward, and everyone else, here is a question:

If longdesc is reinstated into HTML would you prefer having a default
indicator to be  a MUST or a SHOULD or a MAY?


Best Regards,

Laura L. Carlson
Received on Thursday, 7 April 2011 18:00:20 UTC

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