W3C home > Mailing lists > Public > www-validator@w3.org > September 2005

Re: note from Prof Knuth

From: Liam Quinn <liam@htmlhelp.com>
Date: Tue, 20 Sep 2005 21:47:21 -0400 (EDT)
To: Maggie McLoughlin <mam@theory.Stanford.EDU>
cc: www-validator@w3.org
Message-ID: <Pine.LNX.4.44.0509202116510.21815-100000@localhost.localdomain>

On Tue, 20 Sep 2005, Maggie McLoughlin wrote:

> I think I understand the reasoning in your message except
> for one thing: Why could it possibly be right to insist on
> the "alt" attribute always being present, instead of letting
> alt="*" be the default?? You said you wanted to save bandwidth.
> But I'd have to add many thousands of characters to my pages,
> just to put in a default that every browser obviously already
> has built in.

Some browsers distinguish between alt="" and an omitted "alt" attribute.  
The reason is that, historically, the omission of the "alt" attribute was
most likely to indicate that the author didn't bother to think about
alternative text.  It's very useful for non-graphical browsers to be able
to distinguish between purely decorative images and alt-less images that
may have important meaning.

For example, Lynx displays the bottom part of Prof Knuth's home page in
the following way:

  * Did you borrow a video from me? [new.gif] [new-eagle.gif] [newave.gif]  

      [border.gif] [blank.gif] [blank.gif] (don't click here) [blank.gif]
  [logo.csd.gif] Stanford Computer Science Home Page 

     (Netscape-HTML checked) [count.cgi?df=knuth-index.dat|sh=0]

If you used alt="[New!]" for one of the "NEW" images, that would
communicate the meaning more cleanly.  For the other images without "alt"  
attributes, I suggest alt=""; then Lynx would know that the images are
purely decorative, and it would not render the distracting [foo.gif]

> You suggested that I try
>   valign="middle"
> in place of
>   align="absmiddle".
> But I just tried it, and got the error message
>   there is no attribute "valign"

He should have written align="middle" instead of valign="middle".

> Also, I suspect you could tell me how to insert a few lines
> of CSS code so that your validator automatically appends
> alt="*" to every img that doesn't already have an alt attribute.

It's not possible to do that with CSS.  CSS is concerned with
presentation; the "alt" attribute is content.

Liam Quinn
Received on Wednesday, 21 September 2005 01:47:17 UTC

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