2.4 Ensure that dynamic content is accessible or provide an alternative presentation or page

Rationale

Dynamic content may be inaccessible for a variety of reasons. Some types of dynamic content, such as audio or video, are not supported by older browsers or text-only browsers. Frames are also not universally supported by browsers and other user agents. Screen readers can struggle with continually updating dynamic content, such as scrolling news tickers. They may also fail to react to frame updates in the same way that they would to a page transition or refresh, which may cause problems. Users who have slow connections may disable browser features required to process and display dynamic content in order to speed up download times.

Directions and Techniques

Use the LINK element to direct users to alternative formats

The LINK element may also be used to designate alternative documents. Browsers should load the alternative page automatically based on the user's browser type and preferences. See the WAI recommended techniques for the Link element and alternative documents

Use scripts to automatically detect different browsers and present appropriate versions of web pages

A "browser detect" is a script which can detect the type of browser used by a visitor to a site. If a browser detect is used in combination with alternative versions, it is possible to present the user with a version of the page which works well in their browser. Note that it is not possible to detect if the user is using a screen reader because they are not browsers.

Use server side scripts to generate alternative pages on demand

Server side scripts, such as Java servlets, or PHP can be used to create alternative presentations of a page if the user requests one through their browser. The benefit of providing alternative pages in this way is that there is no requirement to maintain different "versions" of a website which reduces the maintenance effort and ensures that up to date content is delivered to the user, regardless of the version they select.

Provide a clear link to alternative version(s) at the top of each page

Providing the link at the top of the page means that the user does not have to wade through inaccessible content to view the alternative version. You should also provide a link to allow the user to navigate back to the original version.

Consider using user profiles for frequently visited pages

If the site contains information or services which a user is likely to use on an ongoing basis, consider providing them with the option to save a profile, which would save their preferences for the version of pages they need. This will save them the trouble of navigating to an alternate version each time.

Write scripts that transform gracefully

A script is said to transform gracefully if the information provided by the script is made available to the user, even if their browser or user agent does not support scripts. The presentation may vary and may not be as elegant as it would be if the users browser supported scripts but the information or functionality should be available. See the WAI recommended techniques for graceful transformation of scripts

If you use frames, provide a way to navigate to a non-frames version

You should write HTML which allows users of browsers which do not support frames to navigate to a version of your site which does not use frames. See the WAI recommended techniques for writing for browsers that do not support frames

Provide an offline equivalent

If it is absolutely impossible to deliver an accessible page, provide an offline service, delivered by trained personnel. Provide contact details such as email, telephone number, postal address and information on getting to the location if this is needed. This way information or services can be delivered over the phone, by correspondence, or in person. Because people often access the web at times outside normal office hours or from other time zones, you should consider offering this service on a 24 hour basis.

How you could check for this:

Test with different browsers and user agents

Testing with the widest variety of browsers and user agents, such as screen readers, Braille devices, etc. will show if an alternative presentation is required. If you provide alternative versions of content, test these to ensure that they are accessible. If you do not have direct access to this technology, get someone who knows how to evaluate the site to do so with these user agents.

- View WAI checkpoint 6.5