Re: Need differentiator between "no alt text provided" and "no alt text necessary"

On Fri, 6 Feb 2009, James Craig wrote:
> Ian Hickson wrote:
> > The spec already says:
> > 
> > # If the src attribute is set and the alt attribute is not
> > #   The image might be a key part of the content, and there is no textual
> > #   equivalent of the image available.
> > #
> > #   [...] the user agent should display some sort of indicator that there
> > #   is an image that is not being rendered [...]
> > 
> > ...which seems like a more accurate statement (since we can't know that
> > the author didn't know alternative text, it might just be that the
> > document is non-conforming).
> 
> Then the easiest edit might be to change:
> 
> "the image might be a key part of the content"
> 
> to:
> 
> "the image is a key part of the content in a conforming document"
> 
> or perhaps to:
> 
> "the image is a key part of the content in a conforming document, and 
> might be a key part of the content in a non-conforming document"

This is text intended for user agents. How could a user agent distinguish 
one case from the other?

I've added a note that says:

   In a conforming document, the absence of the alt attribute indicates 
   that the image is a key part of the content but that a textual 
   replacement for the image was not available when the image was 
   generated.

Does that help?


> I'm more concerned with the first part of #6, now trimmed and quoted 
> here:
> 
> > > 6. If no caption information can be determined from the previous 
> > > steps, user agents MAY assume the image is a key part of the content 
> > > lacking a textual equivalent in the document…
> 
> This addition and/or the edit listed above ("the image is a key part of 
> the content in a conforming document") would appease my concerns.

What does this require? Could you describe a test page that demonstrates 
how to test whether a user agent is complying to this requirment or not?

There's no point adding requirements that aren't testable.

-- 
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'