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Re: LONGDESC in HTML5?

for

From: Jukka K. Korpela
Date: Sep 25, 2010 1:30PM


Vlad Alexander (XStandard) wrote:

> Steve wrote: "I cannot disagree more. the content of the alt
> attribute can be and is many things"
>
> I don't see that. It's a really simple concept and if we keep it
> simple, people will then use it correctly.

The alt attribute has been defined in a simple manner, though with some
contradictions (calling it both "replacement" and "description"), but this
has not made people use it correctly.

There are many cases where it is very obvious what the alt text should be -
though authors often omit alt attributes or write something nonsensical in
them.

The problems start when no single word and no short phrase, or even a
paragraph, can act as an adequate replacement for the image. If the image is
a complex graph, or an artistic painting, or a photograph of a person, then
it should be obvios that _no_ text can be an adequate replacement. It's not
about alt, it's not about longdesc, it's about images.

A document containing an image that is _inherently_ visual content - as
opposite to a decorative ornament or styled text, for example - should at
least inform a user who does not see the image about this. It's all wrong to
provide some textual replacement or explanation or annotation as if it told
the whole story (like simple alt texts for simple images often can tell,
e.g. when the image is just text in image format).

> Steve wrote: "if the image is a photograph, diagram, illustration,
> cartoon, chart the alt may be a short description of the content."
>
> That fits with the definition of alt as a textual replacement for an
> image.

No it does not. If you think it is, you are obscuring the role of alt texts
that really act as replacements. An image button with text "Go" in it has
the textual replacement "Go", undoubtedly. But if you have a photograph of a
house and you write alt="photo of a house" (or alt="(photo of a house)",
which I would prefer), you are not writing an adequate replacement - just
giving a hint. (It's no more a replacement than the words "A poem" would
constitute a replacement for a poem.) In practice, such alt texts are
usually the best we can do, even though it does not conform to the simple
idea of alt as replacement.

If the photo is relevant content, as opposite to mere decoration or
mood-creation, then you might write a long passage of text explaining what's
in the image, mentioning the features of the house and the surroundings that
are relevant. But that's really a matter of content creation. In effect, you
would be creating textual content that is somehow _parallel_ or
_alternative_ to the image. It might say a lot less, but also a lot more.
The image itself would not say what is relevant in it; the text might
concentrate on features that are meant to be essential but are missed by
someone who only sees the image.

If parallel or alternative textual content is created, then it would be all
wrong to use alt or longdesc for them. Instead, graphic and textual content
should both be presented in some manner that makes it easy to understand
their relationships and to access either or both of them

> It all depends on the context (surrounding text). At this link
> I provide examples where alt is not a short description of a chart
> but instead text that is a substitute for an image to make
> surrounding context comprehensible.
>
> http://rebuildingtheweb.com/en/how-do-we-save-longdesc/#c20100824114946

That's a good example of parallel or alternative content: a graph versus a
table. It's often a good idea to provide both, because people may prefer one
or the other (or both). It's counter-productive to hide the table behind a
faulty plastic imitation of a link, i.e. the longdesc attribute. Instead,
the author should decide which presentation is primary (and provide a
normal, descriptively written link to the other), or maybe include both of
them in the flow of normal content.

(In general, a table of data and a graph of the "same" data does not have
exactly the same content. A graph tends to have less details and less
accuracy. This is no problem if you think of them as a parallel
presentations, but it becomes a problem if you want to present one of them
as a replacement or description of the other.)

--
Yucca, http://www.cs.tut.fi/~jkorpela/