HTML and CSS Reference
Forms written in markup are preferred to Flash forms. However, if you have to use Flash forms on your site,
the following guidelines should be considered. Flash controls must be understood out of context. To achieve this,
control labels can be changed via scripting to provide additional information. Similar to their markup equivalents,
the required fields of Flash forms must be clearly indicated. Related Flash form controls must be grouped together to
provide semantic meaning. Flash forms must be validated on the client side. If errors are found, a description must be
added to the controls containing invalid data. Flash form controls must have an associate text label (for example, via
auto labeling). Only CheckBox and RadioButton components get labels by default.
There must be an option to pause scrolling Flash contents controlled by a script.
Blinking of Flash contents must be controlled by scripts to stop within a maximum of five seconds.
Hyperlink anchors must always have a text description that clearly identifies the purpose of the link. Links must
apply the title attribute to provide additional link text. Hyperlinks must have a descriptive alternate text that clearly
indicates the purpose of the link.
Additional link text added for advanced screen reader and Braille display support can be hidden using CSS
selectors (without visibility:hidden or display:none ). This link text can also be applied in combination with a
style switcher. Repetitive content must be avoided.
A control must be added to the top of each web page providing an alternate page version with link texts that are
sufficient to determine their purpose even without context.
The purpose of a link must be clear even without context (applying a descriptive link text), and the container
context (paragraph, preceding heading, list item, table cell, and its associated table heading) must also be written in a
way that further improves the clarity of the purpose of the link.
The minimum contrast ratio of 3:1 should be ensured between link colors and text colors. Moreover, additional
visual cues must be provided on focus for links and controls where color alone is used to identify them.
Destination URIs are generally not descriptive enough. The link text Read more... is, for example, not sufficient
to understand a link. If the description precedes the link in the same sentence, such link texts can be understandable,
however, screen readers would still read “Read more”. The link purpose must be identified using the combination
of link text and the text of the enclosing sentence to ensure a logical text flow for screen readers. Link text changed
dynamically upon context must be provided whenever necessary.
Links should be added to all web page elements and objects that do not support long descriptions as attribute
values. The links must be next to the nontext content. The location of the long description must be indicated in the
short description (if applicable). For example, the short description of an image provides the text “Comparison of
smartphone operating systems—see details below,” while the long description below the image states “In Figure 1,
you can see the market share of smartphone operating systems, including Android, iOS, Windows Mobile, and
If a web page contains blocks of repeated content such as navigation links or table of contents, a link must be
added to the beginning of the blocks that allows users to bypass them. The top of the web page must contain links to
the different sections of the content.
Dialog messages must be device-independent. Pop-up windows should be eliminated whenever possible. If a
new window cannot be eliminated, an advanced warning may be provided. To avoid confusion, new windows opened
on user request with the target attribute may have a proper link text clearly indicating that the content will be opened
in a new window. As a general rule, however, links should be opened in the same window rather than a new window
or tab. While this approach contributes to accessibility, it might lead to loss of visitors (if you point to an external site
and the visitors forget to return to your site