- From: Leif Halvard Silli <lhs@malform.no>
- Date: Wed, 11 Feb 2009 03:59:20 +0100
- To: Jon Barnett <jonbarnett@gmail.com>
- CC: HTML WG <public-html@w3.org>
Hi Jon, Jon Barnett 2009-02-10 21.52: > On Tue, Feb 10, 2009 at 11:37 AM, Robert J Burns <rob@robburns.com> wrote: >> On Feb 9, 2009, at 8:32 PM, Ian Hickson wrote: >> >>> As far as I can tell we already have consensus on alt="" being required. >>> (With one or two exceptions, the spec requires alt="" to be present. The >>> exceptions are machine-checkable.) >>> >> I can't imagine at all how you think these could be machine-checkable >> criteria when it comes to omitting alt. Could you tell us a little about >> what you're thinking? > > There are three bullet points in 4.8.2.1.9 that are machine-checkable when > @alt is omitted. The <figure> and <article><h1> cases are pretty > semantically specific. The @title case is a little less specific. (There > may be more cases where @title may be present but don't match the semantics > for when @alt is omitted - key part of content with no suitable alternate) > > Does that make sense? I think the draft has moved in a right direction. Comments: A) Below you talk about "warning messages". Hence, do you agree that the machine-checkable conditions, when met, should, in Charles' words[1], be considered "conforming but not recommended"? B) W.r.t. the non-empty @title condition: Do you have any valid usecase for where an empty @alt in combination with an non-empty @title, should be the right thing? IMHO such cases do no exist. Semantics and machine-checkability should thus be equal whether @alt is empty or un-present: <img alt="" src=x title="Photography: Mr Xyz." > <img src=x title="Photography: Mr Xyz." > If author tools, including validators, treat both empty @alt and un-present @alt as "conforming but not recommended" for the machine-checkable conditions, then, in order to discern beetween alt="" as a "decorative image signal" and alt="" for images which are "key part of the content", the author only needs to consider whether the <IMG> contains a non-empty @title or not. Thus, un-present @alt-s as a private signal to the author himself that the IMG is key part of the content, aren't really needed, unless non-empty @title-s are very much unwanted. And perhaps those usecases are not not worth catering for? It would eventually only be the figure/section case that could benefit. C) The only difference I see between the two <IMG> elements above, is w.r.t. the expectance of content-repair: The latter is more likely to be semantically repaired for the lack of @alt, than the former likely to be semantically repaired for the lack of content inside the @alt. I think that UAs should treat both cases the same way w.r.t. content-repair. Doing so would not break the Web. >> To me the easiest way to make this machine checkable is to remove those few >> conditions that allow the alt attribute to be omitted and always require the >> attribute (of course allowing authoring tools to produce non-conforming >> documents when authors fail to provide conforming alt text as any other case >> when an author uses an authoring tool to produce a non-conforming document). > > And then in doing so you make the semantics of those more ambiguous and less > machine-checkable (irrelevant vs. relevant images) - unless we go back to > the discussion of adding extra markup for those cases (another thread, I'm > sure). > > As it stands, machines can give better error and warning messages for <img> > elements covering more varied use cases. I agree that the current direction can help authors to think about what they are doing - it isn't only a simple "add a empty alt in order to stay valid". However, it seems to me that it is possible to go much further. For instance, it should be machin-checkable whether the img@alt is identical to the figure caption etc. [1] http://www.w3.org/mid/op.uo350sj3wxe0ny@widsith.local -- leif halvard silli
Received on Wednesday, 11 February 2009 03:00:02 UTC