# Re: Images and alternative text

From: Leif Halvard Silli <lhs@malform.no>
Date: Sat, 09 Aug 2008 01:33:13 +0200
Message-ID: <489CD7B9.9000100@malform.no>
To: Philip Taylor <pjt47@cam.ac.uk>
CC: Dave Singer <singer@apple.com>, "public-html@w3.org" <public-html@w3.org>

Philip Taylor 2008-08-08 20.43:

> Dave Singer wrote:

> It's not fundamentally
> different to assuming users will recognise and understand what "Σax²"
> means, except that it's a different choice of syntax.

TeX/LaTeX is more than a different syntax. It also uses other
symbols than the normal math symbols.

> (Some users won't understand one or the other or both of those syntaxes,
> just like some won't understand the surrounding English prose or the
> concepts being explained, and that's okay since I would only be writing
> equations for a specialised audience.)

But if you are user friendly, then you allow me to know that you
wrote the equation as TeX code. Then I have the chance to look up
TeX to understand what you meant.

>> Yes, if you want to put Latex in there (or any other text), you'll
>> need to put something before an initial {;  perhaps something that
>> helps you diagnose that it is, in fact, latex source, and not really
>> alt text at all.

hear hear.

>>  Perhaps, even
>> alt="{latex} {x \over y} = {1 \over {y \over x}}"
>> ?
>
> According to the current HTML 5 spec (as I understand it), that means
> the image is a key part of the content, and there is no textual
> equivalent of the image available, and the kind of image is "latex} {x
> \over y} = {1 \over {y \over x}".

I agree with Phillip's reading of the current spec.

> I believe the LaTeX code *is* a textual equivalent (because it's text
> (being a human-readable string of mostly-ASCII characters) and it has
> equivalent meaning to the rendered image without any complex encoding),
> so that meaning is inappropriate; and the extracted string between the
> outermost "{" and "}" is clearly not what was intended, and it's not the
> kind of image anyway. (The kind would be something like "equation", but
> that's thoroughly unhelpful to users who can't see the image.)

It is *not* a textual *equivalent*.  It is a textual *fallback*.
It is a "if you can't understand the image, perhaps you would like
to read the source code I used to generate it from?"

Of course source code can sometimes be used as fallback.

> Something like alt="LaTeX: {x \over ... }" would avoid those problems,
> but still that's ugly (particularly if you have many equations in a
> single sentence) and redundant (since it's pretty clear when text is
> LaTeX, to readers who understand LaTeX) and it's not entirely obvious
> how to implement this correctly (as you demonstrated by using "{latex}
> {...}" which'll get badly misinterpreted :-) ).

One simple rule could be to say that if the <img> has lang="zxx",
then the @alt="{keyword}" rule won't apply.
--
leif halvard silli
Received on Friday, 8 August 2008 23:34:01 UTC

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