- From: Schnabel, Stefan <stefan.schnabel@sap.com>
- Date: Fri, 18 Apr 2008 08:31:08 +0200
- To: "Jim Jewett" <jimjjewett@gmail.com>, <annevk@opera.com>, <faulkner.steve@gmail.com>, <jg307@cam.ac.uk>
- Cc: "Ian Hickson" <ian@hixie.ch>, <public-html@w3.org>, <wai-xtech@w3.org>, <wai-liaison@w3.org>
Jim, brilliant overview, your case matrix based on Annes list... We use only case 1 (and checks in our Web Dynpro IDE's to ensure that alt and title have been maintained) and case 8 for purely decorative images where alt when flag "isDecorative" is set will be automatically generated as alt="" for our applications (For spacer images generated by the layout managers, alt is always alt=""). I think encapsulating mandatory alt maintenance in toolkits and builder tools is not the solution but an important step to minimize the issues. - Stefan Dr. Stefan Schnabel Accessibility Expert User Experience - Accessibility SAP AG Dietmar-Hopp-Allee 16, 69190 Walldorf, Germany -----Original Message----- From: wai-xtech-request@w3.org [mailto:wai-xtech-request@w3.org] On Behalf Of Jim Jewett Sent: Mittwoch, 16. April 2008 22:25 To: annevk@opera.com; faulkner.steve@gmail.com; jg307@cam.ac.uk Cc: Ian Hickson; public-html@w3.org; wai-xtech@w3.org; wai-liaison@w3.org Subject: alt and authoring practices Anne van Kesteren wrote: > Given that authors make mistakes there are nine > possibilities of authoring images: > 1. <img alt="..."> - available -> Correct usage > 2. <img alt=""> - available -> Incorrect usage > 3. <img> - available -> Incorrect usage > 4. <img alt="..."> - missing -> Incorrect usage > 5. <img alt=""> - missing -> Incorrect usage > 6. <img> - missing -> Correct usage > 7. <img alt="..."> - empty -> Incorrect usage > 8. <img alt=""> - empty -> Correct usage > 9. <img> - empty -> Incorrect usage > It seems your assumption is that on average 9 > is more common than 3 and 6 ... It seems the > assumption from the editor is that on average > all incorrect usage is about as likely We know they aren't equally likely, and it wouldn't matter very much if they were; we also have to consider the cost of being wrong. One of the baseline assumptions is that cases 4-6 (image important, but no alt available) should be quite rare, at least in content that cares about validity. In practice, they aren't as rare as they should be. I don't have exact statistics on the likelihood of an image being decorative, but it is certainly true of the vast majority of images on most pages that I have checked. (It is less true of large images near the center of the page.) Going in the other direction, it is easy to get a bogus "" or a bogus missing attribute, by just not doing anything. It is much harder to get a bogus filled-in attribute. One of the biggest arguments against magic tokens is that some tools might make those tokens the default, so that they would show up when they shouldn't. (And legacy tools would still need to learn about the magic values, so there would be cost regardless of whether or not there was benefit.) So to recategorize your nine cases: real alt alt="" omitted alt information 1 2 3 not available 4 5 6 decorative 7 8 9 Case 1 is proper alt usage. It isn't as common as we would like, but it is the main goal of alt. Cases 2 and 3 (image important, but alt omitted or empty) are unfortunately still pretty common. And since missing the data here matters, AT goes to heroic lengths to recover. Unless it thinks the image was actually a (correct) case 6 or 8... Using an explicit _notsupplied as the authoring tool's default would let the tool say "not my fault", and tell users that it isn't a (correct and common) case 8. Case 4 is bad, but unlikely to happen by chance. When it happens because of cut-and-paste, there really isn't anything we could do to prevent it. When it happens because of a misguided tool, then allowing an explicit _notsupplied (so the tool can say "not my fault") may help prevent the problem. Case 5 is also rare only because the lack of information is rare. But note that the wrongness comes from tools defaulting to alt="" so they output valid (if wrong) HTML. The current draft suggests omitting the alt; it would probably be more useful (in the long run) to let tools default to _notsupplied, so that the images can be flagged for attention (instead of falsely assuming case 8.) > 6. <img> - missing -> Correct usage (Though not correct under the HTML 4 spec.) This is sufficiently rare that, in practice, AT tools rightly assume cases 3 or 9, and then have to guess which error was made (and the costs of guessing wrong) when deciding how heroic to be about finding a replacement on their own. Case 7 is similar to case 4, but a bit more likely in practice -- authoring tools may insert alt text as part of the skins, which can lead to doubled words. Having an explicit _decorative option would at least reduce the temptation to write alt text like "red bullet". Case 8 is correct -- but looks exactly like case 2. Case 8 is more common, but case 2 is more important. Allowing _decorative would make it explicit that this is case 8. Case 9 is wrong, but defensible. If there isn't information, why supply an alt? alt=_decorative is explicit enough to be worth writing. -jJ
Received on Friday, 18 April 2008 06:36:07 UTC