The criteria emanating from the Web Content Accessibility Guidelines issued in May 1999 and the strictness of implementation will depend on the accessibility level of the site documents. The W3C describes it the following way: For those unfamiliar with accessibility issues pertaining to Web page design, consider that many users may be operating in contexts very different from your own:
- Provide equivalent alternatives to auditory and visual content
a. Provide a text equivalent for every non-text element.
b. Provide redundant text links for each active region of a server-side image map.
c. Provide an auditory description of the important information of the visual track of a multimedia presentation.
d. For any time-based multimedia presentation (e.g., a movie or animation), synchronize equivalent alternatives (e.g., captions or auditory descriptions of the visual track) with the presentation.
- Don't rely on color alone
a. Ensure that all information conveyed with color is also available without color, for example from context or markup.
- Use markup and style sheets and do so properly
a. When an appropriate markup language exists, use markup rather than images to convey information.
b. Create documents that validate to published formal grammars.
c. Use style sheets to control layout and presentation.
d. Use relative rather than absolute units in markup language attribute values and style sheet property values.
e. Use header elements to convey document structure and use them according to specification.
f. Mark up lists and list items properly.
g. Mark up quotations. Do not use quotation markup for formatting effects such as indentation.
- Clarify natural language usage
a.Clearly identify changes in the natural language of a document's text and any text equivalents.
- Create tables that transform gracefully
a. For data tables, identify row and column headers.
b. For data tables that have two or more logical levels of row or column headers, use markup to associate data cells and header cells.
c. Do not use tables for layout unless the table makes sense when linearized. Otherwise, if the table does not make sense, provide an alternative equivalente.
d. If a table is used for layout, do not use any structural markup for the purpose of visual formatting.
- Ensure that pages featuring new technologies transform gracefully
a. Organize documents so they may be read without style sheets. For example, when an HTML document is rendered without associated style sheets, it must still be possible to read the document.
b. Ensure that equivalents for dynamic content are updated when the dynamic content changes.
c. Ensure that pages are usable when scripts, applets, or other programmatic objects are turned off or not supported. If this is not possible, provide equivalent information on an alternative accessible page.
d. For scripts and applets, ensure that event handlers are input device-independent.
e. Ensure that dynamic content is accessible or provide an alternative presentation or page.
- Ensure user control of time-sensitive content changes
a. Avoid causing the screen to flicker.
b. Avoid causing content to blink.
c. Avoid movement in pages.
d. Do not create periodically auto-refreshing pages.
e. Do not use markup to redirect pages automatically. Instead, configure the server to perform redirects.
- Ensure direct accessibility of embedded user interfaces
a. Make programmatic elements such as scripts and applets directly accessible or compatible with assistive technologies.
- Design for device-independence
a. Provide client-side image maps instead of server-side image maps.
b. Ensure that any element that has its own interface can be operated in a device-independent manner.
c. For scripts, specify logical event handlers rather than device-dependent event handlers.
- Use interim solutions
a. do not cause pop-ups or other windows to appear and do not change the current window without informing the user.
b. for all form controls with implicitly associated labels, ensure that the label is properly positioned (The label must immediately precede its control on the same line).
- Use W3C technologies and guidelines
a. Use W3C technologies when they are available and appropriate for a task and use the latest versions when supported.
b. Avoid deprecated features of W3C technologies.
c. If, after best efforts, you cannot create an accessible page, provide a link to an alternative page that uses W3C technologies, is accessible, has equivalent information (or functionality), and is updated as often as the inaccessible (original) page.
- Provide context and orientation information
a. Title each frame to facilitate frame identification and navigation.
b. Describe the purpose of frames and how frames relate to each other if it is not obvious by frame titles alone.
c. Divide large blocks of information into more manageable groups where natural and appropriate.
d. Associate labels explicitly with their controls (For example, in HTML use LABEL and its "for" attribute).
- Provide clear navigation mechanisms
a. Clearly identify the target of each link
b. Provide metadata to add semantic information to pages and sites.
c. Provide information about the general layout of a site (e.g., a site map or table of contents)..
d. Use navigation mechanisms in a consistent manner.
- Ensure that documents are clear and simple
a. Use the clearest and simplest language appropriate for a site's content.