Perceivable - Accessibility 编辑

A text description may work, or an accessible data table (see HTML table advanced features and accessibility). See Other text alternative mechanisms for the argument against longdesc.

See Text alternatives for static caption options, and Audio transcripts, Video text tracks, and Other multimedia content for other alternatives.

Decorative images should be implemented using CSS background images (see Backgrounds).  If you have to include an image via an <img> element, give it a blank alt (alt=""). Otherwise, screenreaders may try to read out the filepath, etc.

If you are including background video or audio that autoplays, make it as unobtrusive as possible. Don't make it look/sound like content, and provide a control to turn it off. Ideally, don't include it at all.

Any content structure—or visual relationship made between content—can also be determined programmatically, or be inferred from text description. The main situations in which this is relevant are:

• Text labels and the form elements they describe. These are associated unambiguously using the <label> element, which can be picked up by screenreaders, etc.
• Image alt text. Content images should have text available that clearly describes the image's contents, which can be programmatically associated with it (e.g., alt text), or otherwise is easy to associate (e.g., describes it and is sat right next to it). This should mean that the full meaning can still be inferred even if you can't see the image.
• Lists. If the order of list items is important, use an ordered list (<ol>).

HTML: A good basis for accessibility is packed with information about this, but you should particularly refer to Good semantics, UI controls, and Text alternatives.

Instructions for operating controls or understanding content do not rely on a single sense. This may prove inaccessible to people with a disability related to that sense, or a device that does not support that sense. So, for example:

• "Click the round button to continue"
  The button should be clearly labelled so that it is obvious that it is the button you need to press. If there are multiple buttons, make sure they are all clearly labelled to distinguish their function.
• "Listen to the audio instructions for guidance"
  This is obviously problematic—audio will be inaccessible to those with hearing impairments, whereas text can be read, but also spoken by a screenreader if required.
• "Swipe from the right hand side of the screen to reveal the menu"
  Some users might not be able to swipe the screen, either due to disability or because their device does not support touch. An alternative should be provided, such as a keyboard shortcut or button that can be activated by keyboard or other means.

Note: Conveying instructions solely by color is related, but covered in a different guideline — 1.4.1.

Understanding Orientation 

Follow the list of 53 input fields to programmatically identify the purpose of a field.