The "prime directive" of Web accessibility the number-one item in both WCAG 1.0 and the Section 508 federal accessibility standards that took effect in June 2001 is the requirement to provide "equivalent alternatives" for visual and auditory elements of the Web site. In this chapter, to explore what that means, we begin at the beginning. We start with ALT text, then move on to other kinds of text equivalents; finally, we briefly discuss uses of other media as alternatives to text.
HTML Elements and Attributes Addressed in This Chapter
<img>, <area>, <script>, <applet>
alt, src, longdesc, width, height
Accessibility Checkpoints and Standards Addressed in This Chapter
Web Content Accessibility Guidelines 1.0 Checkpoints
1. Provide equivalent alternatives for auditory and visual content.
1.1. Provide a text equivalent for every non-text element (e.g., via "alt", "longdesc", or in element content). This includes: images, graphical representations of text (including symbols), image map regions, animations (e.g., animated GIFs), applets and programmatic objects, ASCII art, frames, scripts, images used as list bullets, spacers, graphical buttons, sounds (played with or without user interaction), stand-alone audio files, audio tracks of video, and video. [Priority 1]
1.3. Until user agents can automatically read aloud the text equivalent of a visual track, provide an auditory description of the important information of the visual track of a multimedia presentation. [Priority 1]
1.4. For any time-based multimedia presentation synchronize equivalent alternatives with the presentation. [Priority 1]
9.1. Provide client-side image maps instead of server-side image maps except where the regions cannot be identified with an available geometric shape. [Priority 1]
14.2. Supplement text with graphic or auditory presentations where they will facilitate comprehension of the page. [Priority 3]
Section 508 Standards, §1194.22
(a) A text equivalent for every non-text element shall be provided (e.g., via "alt", "longdesc", or in element content).
(b) Equivalent alternatives for any multimedia presentation shall be synchronized with the presentation.
(f) Client-side image maps shall be provided instead of server-side image maps except where the regions cannot be defined with an available geometric shape.