[whatwg] Alt text authoring Re: Conformance for Mail clients

Charles McCathieNevile chaals at opera.com
Sun Apr 22 18:16:19 PDT 2007

On Mon, 23 Apr 2007 01:31:46 +0200, Jon Barnett <jonbarnett at gmail.com> wrote:

> When UAs do what you describe, do they provide a way to download the image
> (text browsers) or indicate that what's missing in an image (screen
> readers)?  What UAs?  Is this different from how they currently behave when
> alt is present but blank?
> This page:
> <!DOCTYPE html>
> <title>IMG test</title>
> <ol>
> <li>Image represents a <img src=PICT0023.JPG alt=tree>
> <li>Image is content <img src=PICT0023.JPG>
> <li>Image is decorative <img src=PICT0023.JPG alt=''>
> </ol>
> Is rendered by Lynx (on my machine) as:
>     1. Image represents a tree
>     2. Image represents is content [PICT0023.JPG]
>     3. Image represents is decorative
> Only in (2) does Lynx indicate that the image is missing.  That's the
> behavior I would expect (even with noalt)
> Neither Firefox nor Konqueror distinguish between (2) and (3) with images
> disabled.

Opera behaves like Lynx here under default conditions.

> "noalt" is a good idea and leaves no ambiguity.

Except that it breaks all backward compatibility. Providing a way to download the image is the job of a user agent (Opera's info panel says that there is 1 inline element - or 3 if I change the URIs to be unique), but I don't see how it comes from markup. (In Opera you can get images with missing or null alt by using the user mode 'alt text debugger' - you can add the user style

  img { min-width:20px ; min-height 20px }

to that if you want to make easier targets for download).

> The current draft does say that a missing alt should be treated as if it's
> blank.  Should that stay the same, or should special semantics be defined
> for a missing alt?

User agents should treat this as an error. There is a procedure described in the User Agent Accessibility Guidelines, which specifies a requirement to handle this case as different from alt="":

2.7 Repair missing content (P2) Techniques for checkpoint 2.7
Allow configuration to generate repair text when the user agent recognizes that the author has not provided conditional content required by the format specification.
Sufficient techniques
The user agent may satisfy this checkpoint by basing the repair text on any of the following available sources of information: URI reference (as defined in [RFC2396], section 4), content type, or element type. Note, however, that additional information that would enable more helpful repair might be available but not "near" the missing conditional content. For instance, instead of generating repair text on a simple URI reference, the user agent might look for helpful information near a different instance of the URI reference in the same document object, or might retrieve useful information (e.g., a title) from the resource designated by the URI reference.
]]] - http://www.w3.org/TR/UAAG10/guidelines.html#tech-missing-alt

The original, plus some more explanation is provided at http://www.w3.org/TR/UAAG10-TECHS/guidelines.html#tech-missing-alt



  Charles McCathieNevile, Opera Software: Standards Group
  hablo español  -  je parle français  -  jeg lærer norsk
chaals at opera.com          Try Opera 9.1     http://opera.com

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