W3C home > Mailing lists > Public > public-html@w3.org > February 2009

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

From: Ian Hickson <ian@hixie.ch>
Date: Tue, 3 Feb 2009 04:52:47 +0000 (UTC)
To: James Craig <jcraig@apple.com>
Cc: Maciej Stachowiak <mjs@apple.com>, public-html@w3.org
Message-ID: <Pine.LNX.4.62.0902030444140.952@hixie.dreamhostps.com>
On Mon, 2 Feb 2009, James Craig wrote:
> 
> Are you referring to the sentence that starts: "If the image is not 
> available or if the user agent is not configured to display the image, 
> then…"?
> 
> If so, that sentence does not address the non-visual equivalent of a 
> displayed image. It only addresses the cases of a broken or missing 
> image, or the inability to display an image. Those cases are necessary 
> but, as far as I can tell, irrelevant to this thread.

Isn't the case you are talking about covered by "if the user agent is not 
configured to display the image"?


> Would you be willing to add this clarification (as previously proposed 
> by Maciej) of how user agent handle images without an alt attribute? 
> Since it's an RFC 2119, I assume it would need to go in a normative 
> section.
> 
> "User agents MAY (or SHOULD) assume images without an alt attribute are 
> a key part of the content lacking a textual equivalent."
>
> That would then clearly indicate the following:
> 
> 1. <img src="…" alt="">		Presentational image.
> 2. <img src="…" alt="foo">		Meaningful image, alt text provided.
> 3. <img src="…">			Meaningful image, no alt text provided.
> 
> Currently case #3 is unclear. It might be a meaningful image with no alt 
> text provided, or it might be something else entirely. I realize that 
> we'll always have authors that do not use alt correctly, but we should 
> have a clear definition of what it means when they do.

I'm glad you agree that cases 1 and 2 are covered. Specifically, they are 
handled by the first two entries in the list after the sentence that says 
"What an img element represents depends on the src attribute and the alt 
attribute".

Case 3 is covered by the next entry in that list, entitled "If the src 
attribute is set and the alt attribute is not".

First, that section defines what this means:

# The image might be a key part of the content, and there is no textual 
# equivalent of the image available.

Then, it says what user agents that _do_ support images must do:

# If the image is available, the element represents the image specified by 
# the src attribute.

(Extra text in the rendering section will elaborate on this.)

Next, it says what user agents that do _not_ support images must do:

# If the image is not available or if the user agent is not configured to 
# display the image, then the user agent should display some sort of 
# indicator that there is an image that is not being rendered, and may, if 
# requested by the user, or if so configured, or when required to provide 
# contextual information in response to navigation, provide caption 
# information for the image, derived as follows:
#
# 1. If the image has a title attribute whose value is not the empty 
#    string, then the value of that attribute is the caption information; 
#    abort these steps.
#
# 2. If the image is the child of a figure element that has a child legend 
#    element, then the contents of the first such legend element are the 
#    caption information; abort these steps.
#
# 3. Run the algorithm to create the outline for the document.
#
# 4. If the img element did not end up associated with a heading in 
#    the outline, or if there are any other images that are lacking an alt 
#    attribute and that are associated with the same heading in the 
#    outline as the img element in question, then there is no caption 
#    information; abort these steps.
#
# 5. The caption information is the heading with which the image is 
#    associated according to the outline.

This is a pretty detailed set of requirements already. Could you elaborate 
on what your proposal:

> "User agents MAY (or SHOULD) assume images without an alt attribute are 
> a key part of the content lacking a textual equivalent."

...is intended to require? How would we test this requirement is being 
followed, as opposed to the other requirements already listed?

-- 
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'
Received on Tuesday, 3 February 2009 04:53:24 GMT

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