Alt? Longdesc? Title? What goes where, especially

问题:

So I've been trying to make my site as accessible as possible (for non-JavaScript users, web crawlers, screen readers, etc), and I hit a large snag.

The site I'm developing is very image heavy. (I draw stupid stuff in my spare time and the site is a sort of a "showcase".) Each page in the site has a single image (or multiple, if context is needed or the image is several panels) that is usually accompanied by a single caption underneath. So when I got to the point where I had to add accessibility options, I wasn't sure what to do. For example, let's say I had an image of a man eating an apple and the joke was there's a worm in it. So the first thing I did was add a ludicrously descriptive alt text since it was the only way to provide an "equivalent" for screen readers.

<img src="appleeat.png" alt="A man bites into an apple. As it turns out, there's a worm in it!">

This seemed okay at first, but then things went awry really quickly when I suddenly found myself needing to add alt text up to 300 characters (!!!) for the more elaborate jokes and images. Not only that, but apparently alt text isn't for descriptions anyway.

So I'm having these problems:

1. Alt text is for equivalents, not descriptions. However, the only way to provide an equivalent in this case is to provide a description.
2. longdesc seems to be more suited for this feat, but longdesc is not supported by any browser (at least, according to W3Schools) even though it does seem to be in the HTML5 specification.
3. <figcaption> seems to be the way to go, but it ends up displaying text underneath the image in question, which is definitely not very appealing for my site, especially if I want to add additional captions and context in <p> tags or something.

So what do I do? What would I put, and where? I'm totally stumped on this, and frankly I'm not certain that making a site based entirely on images accessible to people who can't see very well is a good idea.

回答1:

The alt attribute is for alternative text, i.e. textual replacement for an image, so in the example, it is adequate if it reasonably tells the same story as the image. In reality, most images cannot have texts that are full “alternatives” or “replacements”; it’s usually a matter of capturing some of the most essential message, if possible.

An alt text can be of any length. The statement that alt texts should not be descriptions does not mean that it cannot be detailed if needed. The point is that there are too many descriptions that say something about an image without conveying its message (like “big red bullet” or “A man in a canoe”).

The longdesc attribute is supported by some software but highly debated and not part of W3C HTML5 CR but being developed as an independent “extension”.

The figcaption element is for captions presented along with an image. It does not address the issue of alternative text at all. It is meant to be presented to the user, whether he sees the image or not.

回答2:

If you want to provide complex alternative text (where "complex" could mean: containing lists, tables, audio/video etc.), you could either use an img element with a longdesc attribute, or an object element instead of img.

longdesc

In HTML 4.01, longdesc is part of the specification. In HTML5, it was removed, and is now developed as an HTML5 extension (but it’s currently only a Working Draft from 2013 Update: it became a W3C Recommendation).

Problem: You would either have to include the content on the same page, but then you shouldn’t visually hide it (as not only screen reader users may want to access this content). Or you would have to add separate pages for the content (but then search engines won’t relate this content to the image, i.e., you miss on ranking potential).

object

The object element can be used for any kind of media. Its content is the fallback content, which allows you to use markup for the alternative text.

<object data="appleeat.png" type="image/png">
  <!-- the alternative content goes here -->
  <p>A man bites into an apple. As it turns out, there's a worm in it!</p>
</object>

回答3:

Here’s some discussion of alt text that might apply to your situation:

• http://webaim.org/techniques/alttext/#context.

Although I agree with @Jukka that long alt text isn’t a problem in itself. It’s true that “alt text isn't for descriptions”, but only because alt text is for equivalent content. If the equivalent content to a particular image is a description of it, then that’s fine.

It’s just that for lots of images used on the web, that’s not true. For example, the best alt text for the Stack Overflow logo at the top of this page wouldn’t be

The Stack Overflow logo: an abstract in-tray overflowing with paper, followed by the word “stack”, and in bold, the word “overflow”

It would just be “Stack Overflow”, because that provides an equivalent experience for a partially-sighted person (i.e. it tells them which website they’re on).

But if your images are cartoons, I guess writing alt text for them is a bit like doing audio descriptions for movies. You need to be more descriptive if you want to provide an equivalent experience. It’s certainly a challenge, especially if you don’t have experience, or partially-sighted users to discuss it with.

Joe Clark, in his book “Building Accessible Websites”, discussed describing images:

• http://joeclark.org/book/sashay/serialization/Chapter06.html#h2-2290

And even providing alt text for comic strips, although his example is for dialogue-heavy strips, and I’m not sure what sort of experience it provides in today’s screen readers:

• http://joeclark.org/book/sashay/serialization/Chapter06.html#h2-4240

回答4:

I think adding in descriptive text in a <figcaption> is a good idea. There is of course the problem with browser support, this should be able to be addressed with CSS:

figcaption { display: block; }

You could then hide this text by default figcaption { display: none; } and include a link somewhere that will refresh the page with the captions displayed through an alternative style - figcaption { display: block; }

This option then eliminates the need for javascript solutions and only gives captions to those that specifically request them.

You could maybe set this up with a little bit of php:

<head>
    <style type="text/css">
        <?php if(isset($_GET['CaptionDisplay']))
            {
                echo 'figcaption { display: block; }';
            }else{
                echo 'figcaption { display: none; }';
            }
        ?>
    </style>
</head>

HTML Link - <a href="example.php?CaptionDisplay=true">Show captions</a>

This is completely off the top of my head :) Let me know if I can better explain anything.

回答5:

I think "equivalent experience" is kind of subjective, and I can attest from experience that many accessibility guidelines, while well-intentioned, aren't correct. For a screen reader user, just seeing the Stack Overflow alt tag logo wouldn't provide an equivalent experience to a sighted user. You should always describe any alt tags properly. I don't think having a longer alt text is necessarily bad, but if it gets too unwieldy, you could build a separate section in plain text. Thank you for taking the time to make your site accessible. Screen reader users do appreciate inclusive design and the thought-out descriptions.