HTML and CSS Reference
In-Depth Information
A text cue must be added to colored form control labels to combine color and text or character cues to convey
information. For example, required field labels represented in red can be quickly recognized by most people, but not
all people can see colors. However, they can still read text cues or listen to them.
A description must be associated with form controls indicating context changes in advance. A submit button
must be used in order to allow users to explicitly request changes of context. The aria-required WAI-ARIA property
can be used to indicate that user input is required before submission. Text descriptions must be provided to identify
required fields that were not completed.
Table Requirements
Tabular information must be presented with the table element. Table captions must be associated with tables by
using the caption element. Data cells and header cells must be associated with the id , header , and scope attributes
in tables. In Flash, the DataGrid component must be used to associate column headers with cells. These components
must have a caption text. The summary attribute must be applied on the table element to provide a short description
of the table (which is used by screen readers).
User Control Requirements
Every web site's functionality must be accessible not only with pointing devices such as a mouse but also with the
keyboard. This also holds for Flash contents (using the click event on standard components).
A control must be provided on all web pages that allows users to stop moving or blinking contents, or prevent
automatic content updates.
Both a pause and a restart option must be provided for all automatically refreshing or disappearing contents such
as banners or flash headers. A link to the alternate content for the time-based media must be placed immediately next
to the nontext content. Users should not be forced to complete any activities within time limits. Users must always be
warned by a script if the time limit is about to expire. This also holds for Flash content.
Users must always have the option of setting time limits to ten times the default value. The option for extending
the default time limit also applies for Flash contents. There must be a mechanism to turn off time limits.
The actions of markup elements such as anchors and form elements must be keyboard-accessible. Event
handlers must be device-independent and allow not only the mouse but also keyboard access to full content
functionality (for example, drag and drop). This can be achieved using redundant keyboard and mouse event
handlers. The same holds for Flash contents as well as all scripting functions.
Web servers that require user authentication often terminate sessions for security reasons after a certain period
of time spent without user activity. If the user cannot provide the input quickly enough, the session times out before
data submission, and reauthentication is required. Servers should store such data in a temporary cache and retain
them after a successful user reauthentication, so the user can continue filling in the form rather than starting it all over
again, because all previously entered data is restored. Reauthorization pages may hide and encrypt user data.
Context changes must apply predictable actions. For example, if data entries of a form cannot be presented on a
single page, the second page should not be loaded automatically after the user presses the Tab key on the last entry of
the first page, because it can confuse screen reader users, which must be avoided.
Automatic redirections should be eliminated whenever possible. Both client-side ( meta refresh ) and server-side
(HTTP response) redirections have accessibility issues that can confuse users.
Certain user interface components are highlighted by some browsers when they receive focus. For example, a
form input is slightly highlighted in Google Chrome and strongly highlighted in Safari by default but not highlighted at
all in IE, Firefox, and Opera (Figure 10-10 ).
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