HTML and CSS Reference
Figure 10-10. Default browser highlighting of the same input field in Firefox and Safari (the second text input is
Since highlighting varies from component to component and from browser to browser, the high visibility of focus
indicators should be ensured by web developers.
Form components, links, and all elements with a tabindex attribute greater than 0 can receive focus. However,
the default focus indicator of some platforms is not highly visible and may be difficult to see against certain
backgrounds. The visibility of focus indicators should always be ensured.
Nonessential alerts are optional. Ideally, users are not disturbed with unnecessary modal pop-up windows
(dialog windows that require the user to click the OK button to disappear).
Time-based media such as presentations must always have an alternate textual version or description.
Automatically updated contents may be eliminated and a mechanism provided to postpone automatic content
update. Moving and scrolling texts must also be available in a static page section or window
Live Media, Audio, and Video Requirements
Prerecorded synchronized media such as video clips must have captions. Sounds can be played on user request only.
Sound effects must automatically be turned off within three seconds. Additionally, an easily discoverable control must
be located near the beginning of the page for turning sound on/off. Flash contents must also have a control for the
In Flash movies, screen reader detection with the flash.accessibility.Accessibility.active property can be
used to turn off sounds that are played automatically if assistive technology is used (by default, the sound can still be
Nonspeech sounds in audio files may be at least 20 dB lower than the speech audio content.
An additional, user-selectable audio track must be provided with audio descriptions.
A spoken version of the text can significantly improve site accessibility because it is more accurate and
perceivable than the speech of screen readers.
Live audio-only contents may have text alternatives. This can be achieved by a real-time caption service with
a trained human operator who can type the text with small delay. Note that such services are very rarely used in
A link to a text transcript of a prepared statement or script may be provided for scripts followed by live audio
contents. These scripts can be more accurate and complete than live transcriptions; however, care must be taken to
ensure correct synchronization.
Accessible alternatives must be provided for time-based media presenting audio-only or video-only contents.
A descriptive label must be provided for live audio-only and live video-only content.