HTML5提供了哪些可访问性改进？ [英] What improvements to accessibility are offered by HTML5?
问题描述
HTML5对HTML 4.01或XHTML 1.0提供了什么样的好处，以确保可访问性？
- 可能还有很多：
关于HTML 5中可访问性的最重要的事情并不是哲学上的变化。 HTML 5遇到了一些麻烦，鼓励网络作者不要将信息放入普通用户看不到的地方，例如alt和summary属性，而是鼓励他们将信息放入正常的正文文本中。这个想法是：（a）隐藏在这些属性中的信息通常对于有视力和无视力的人都是有用的;（b）如果作者在维护和测试他们的页面时可以看到这样的文本，他们更有可能保留它正确且最新，比隐藏起来更新。因此，例如，它定义了一个图元素，允许图片和标题（即图例元素）相互关联。
在许多情况下，对于以前放置在alt属性中的文本放置在图例元素中，实际上更好一些，但理论上应该注意它们是不同的 - alt是 文本 - 图例是辅助文本。这同样适用于表格上的摘要属性和标题元素。鼓励使用caption元素通过摘要属性，但它们不提供完全相同的用例。这最近一直是一个实质性争议的主题，目前的情况是，@summary被定义为过时但符合，无论如何。
也许HTML 5中功能方面的最佳可访问性收益是正在进行的将WAI-ARIA，无障碍富互联网应用程序套件（ http://www.w3.org/WAI/intro/aria ）。
我相信有一种隐式的新算法将表格单元格与其标题单元格相关联以供屏幕阅读器使用，这可以节省必须明确指定关联的工作。
还有一些问题。新的视频和音频元素没有HTML级别后备 - 假设可访问性回退将直接嵌入到视频和音频文件中。这是一个持续争议的问题。作为网络作家亲自讲话，我知道如何将音频文件的副本写入HTML，但我不知道如何将备用文本嵌入到预先存在的音频文件中。因此，虽然它可能是一个将回退放入音频文件的优秀解决方案，但在很多情况下，这种情况不会发生，而那些无法直接体验音频的人将成为失败者。
新的canvas元素目前也是一个很大的可访问性问题。尽管一些人有关于该做什么的想法，但画布是否能够具有真正可以接近的等效物并不是一个明证。
What benefits are offered by HTML5 over HTML 4.01 or XHTML 1.0 Strict for accessibility?
Some stuff that comes to mind - there's probably lots more:
The most important thing to note about accessibility in HTML 5 is not so much features as a change in philosophy. HTML 5 goes to some trouble to encourage web authors not to put information into places where ordinary users can't see it, such as alt and summary attributes, and instead encourages them to put the information into the normal body text. The idea is that (a) often the information hidden in these attributes is useful to sighted and non-sighted people alike and (b) if the author can see such text when maintaining and testing their page, they're much more likely to keep it correct and up-to-date than if it's hidden away. So for example, it defines a "figure" element that allow a picture and caption (i.e. the "legend" element) to be associated with one another.
In many cases, it is better practically for text that would previously have been put in the alt attribute to be put in the legend element, although it should be noted that theoretically they are different - alt is equivalent text - legend is auxiliary text. The same applies to the summary attribute and caption element on tables. Use of the caption element is encouraged over the summary attribute, but they don't serve exactly the same use cases. This has recently been the subject of a substantial dispute, with the current situation being that @summary is defined as being "obsolete but conforming", whatever that means.
Perhaps the best accessibility gain in terms of features in HTML 5 is the on-going process of integrating WAI-ARIA, the Accessible Rich Internet Applications Suite (http://www.w3.org/WAI/intro/aria).
I believe there's a new algorithm for implicitly associating table cells with their headers cells for screen readers to use which may save work having to specify the associations explicitly.
There's also some problems. The new "video" and "audio" elements have no HTML level fallback - it's assumed that accessibility fallback will be embedded directly into the video and audio files. This is a matter of ongoing dispute. Speaking personally as a web author, I know how to write a transcript of an audio file into HTML, but I don't have a clue how to embed fallback text into a pre-existing audio file. So while it may be a superior solution to place the fallback into the audio file, it many cases it's just not going to happen, and those who can't experience the audio directly will be the losers.
The new "canvas" element is also currently a big accessibility problem. Although some there are ideas about what to do, it's not at all clear whether "canvas" can ever have a truly accessible equivalent.
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