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Re: dated WD snapshot of alt techniques document

From: <chaals@yandex-team.ru>
Date: Fri, 17 Oct 2014 11:42:30 +0200
To: George Kerscher <kerscher@montana.com>
Cc: 'HTML Accessibility Task Force' <public-html-a11y@w3.org>, DIAGRAM Standards <diagram_standards@benetech.org>
Message-Id: <8631413538950@webcorp02g.yandex-team.ru>
- janina@, faulkner.steve@, public-html-admin@, plh@, mike@, w3b@, rubys@, Paul.Cotton@, mjs@, public-pfwg@, jbrewer@

Hello George,

16.10.2014, 17:24, "George Kerscher" <kerscher@montana.com>:
> Dear Janina and Steve,
>
> With cc to the DIAGRAM Standards working group and Judy Brewer,
>
> The Association of American Publishers asked for guidance with images in
> their publications. Of course, we based our recommendations on WAI developed
> best practices. The publishers are looking for guidelines that directly
> relate to the production of digital books using the EPUB specification,
> which builds on W3C technologies. You can find what we produced at:
>
> http://diagramcenter.org/59-image-guidelines-for-epub-3.html
>
> One of the tasks this year in the DIAGRAM Project is to make sure that we
> are in harmony with W3C/WAI best practices. It seems that šwith the working
> draft mentioned below, now is a good time to initiate this discussion.

Indeed.

In particular I note that there is a technical error in suggestion 2d of that document.

aria-describedby only provides plain text, created by concatenating all the text labels in the description, according to the Usar Agent Implementatin Guide, which is a W3C Recommendation [1]. So if you use it for MathML, tables, etc, you're likely to produce something very hard to understand at best, and garbage at worst.

This is one of the issues longdesc [2] is meant to solve, by being a link rather than degenerating to a simple text property.

I would also note that while assistive technologies often handle ARIA well now, they are very poorly implemented in standard browser user interfaces. Which means that for example a user with low vision, relying on standard zoom, but needing s description to make sense of an image they cannot see well will have no way of finding it if the description is hidden. 

Primarily for this reason (but also because it can introduce the "invisible metadata" maintenance problem) I suggest that hiding the description in a page is not a good practice, and that you should generally recommend against doing so.

Again, the longdesc spec seeks to address this issue, by explicitly requiring that browsers provide access in their own interface, whereas while ARIA in theory allows that it only requires information to be passed to special APIs.

[1] http://www.w3.org/TR/wai-aria-implementation/#mapping_additional_nd
[2] http://www.w3.org/TR/html-longdesc

cheers

Chaals

--
Charles McCathie Nevile - web standards - CTO Office, Yandex
chaals@yandex-team.ru - - - Find more at http://yandex.com
Received on Friday, 17 October 2014 09:43:04 UTC

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