使用aria标签作为内容是否不好？

Question

I've a case where I'd like to use aria-label to give screen-readers access to the (CSS pseudo-)content. Something like this:

 [data-pseudo-content]::before { content: attr(data-pseudo-content); } 

 <h1 aria-label="This is the title" data-pseudo-content="This is the title"></h1> 

Is it bad to use aria-label for content rather than a label for the content? Also, would some screen-readers read This is the title twice?

Answer 1

To the best of my understanding, aria-label can be applied in some situations to change or enrich the accessible name of an element (= the textual representation that will be outputted to the user, either by speech or by braille). The amount of influence of aria-label or aria-labelledBy on the accessible name depends on how much information the node contains and its type or role itself.

Your example (confirmed with NVDA on Windows 8.1 in Chrome 42 and Firefox 36) doesn't make much of a difference for a screen reader, as it will follow a set of rules to determine the accessible name. In my experience, a screen reader will - among others - give priority to the containing text if other conditions (role) fail. If the node would happen to be empty and other alternatives are not available, a screen reader will render aria-labelledBy or aria-describedBy as the accessible name if provided. Otherwise it will be ignored.

Luckily in your case, the ARIA standard also covers :before and :after as part as the algorithm for determining the accessible name. You can read more about how the accessible name is being computed at the spec: http://www.w3.org/TR/wai-aria/roles#textalternativecomputation

When would aria-label or aria-labelledBy make a good use? I'm still researching the subject, so I cannot provide a 100% certain answer for the time being. I do, however know that it makes a difference on elements like <input> . You should apply aria-label when there is no visible label available. It might also be useful to know that, whenever aria-labelledBy is rendered, it will always be placed first in the accessible name. This could be useful for form fields, because <label> might not always be rendered first if many attributes are given. aria-label / aria-labelledBy are also useful when you use the contenteditable attribute on an element, to make sure that the content is accessible for screen readers.

Here is a wiki with some examples of how aria-label / aria-labelledBy could be applied (search on page for those words): http://www.w3.org/WAI/GL/wiki/Category:ARIA_Techniques

Remember: the best way to figure out what works and what doesn't, is by playing around with a screenreader. I have not been able to test with other screen readers (apart from NVDA and iOs VoiceOver for a while), so the implementation on other screen readers like JAWS might differ. Other known screen readers are Windows Eyes and Supernova (though I heard that SN is not good with replacing focus with .focus(), so be careful). It might also be a good idea to test in different browsers, as the accessibility API might differ and give slightly different outputs.