For images and animation, use alt text to provide a brief description, and the longdesc attribute to provide explanations longer than a sentence or two. Longdesc provides an invisible link read by screen readers to a detailed description located on a different Web page.

For audio and video, provide a hyperlink to a trascript plus a description near the play button or link to the clip. Descriptions should generally be longer than transcripts because they need to descibe the setting and action.

For Java applets, provide alt text, and if the applet uses the OBJECT element, provide text descriptions within the element.

Movement attracts the eye. If you draw attention to an element by making it move, you may cause it to seem more important than surrounding images which remain still. If you place animated images near still text, be careful that the animations do not distract the reader. And if you animate text, make sure you control the timing and test to make sure that the text is still readable.

Some animations are used to entertain, but you can also use them to explain. They are particularly good for explaining ideas involving changes in time, position, and/or process.