Each Guideline and each Technique has a priority listed. For the guidelines, the priority refers to the importance of addressing the issue identified by the guideline. For Techniques, there may be a number of techniques used to improve accessibility with respect to this guideline. For example a priority 1 Guideline may have a priority 1 Technique, which MUST be done to provide accessibility, and a priority 3 Technique, which MAY also be done to help address the issue.
Provide alternative representations of all non-text information so that a page may be perceived and used without needing to be seen and without needing to be heard. | |||
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Guideline | Rationale | Techniques | |
1. | Provide alternative text for all images, applets, and image maps, including images used as submit buttons and all of the links within an image map. [Priority 1] | Otherwise, users
who are blind, have low vision, or
have chosen not to view graphics will not know the
purpose of the visual components on the page.
Example Since ASCII art uses characteres to create a visual image there is no way to attach alt-text as with other images. |
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2. | Provide descriptions for graphics, scripts, or applets that convey important information (unless it is already fully presented in the alt-text or accompanying text on page). [Priority 1] | Otherwise, important information presented graphically (charts, billboards, diagrams) will not be perceivable to people with blindness, some people with low vision, and users who have chosen not to view graphics, scripts, or applets or whose browser does not support scripts or applets. |
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3. | Provide textual equivalents (captions) for all audio information. If the audio is associated with a visual presentation (movie or animation), synchronize the textual equivalents with the visual presentation. [Priority 1] | Otherwise, users who are deaf, or hard of hearing, or who have sound turned off cannot perceive the information presented through sounds such as speech, sound effects, and music. |
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4. | Provide verbal descriptions of moving visual information in both auditory and text form (movies, animations, etc.). If the visual presentation is associated with an auditory presentation (e.g., movies), synchronize the auditory descriptions with the existing auditory presentation and collate the text version of the descriptions with the text transcript (captions) of the primary audio track. [Priority 1] | Otherwise, users who cannot see (or look at) the page will not be able to perceive information presented through action, body language, or other visual cues that are not available through the auditory information (dialogue, sound effects, etc.). The collated text version allows access to the information by devices that do not play movies, by people who are deaf-blind. (It also allows all of the content to be accessed by indexing engines.) |
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5. | Use HTML in a way that allows you to provide alternative presentations easily. [Priority 1] | For example, if you use an image as the source of a frame, then there is no simple way to attach alternative text for that image. But, if you use an HTML file as the source of a frame with the image included in that, providing the alternative text becomes easy. (see A-1 for more information about alt-text). |
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6. | Avoid using color to convey information that is not also presented through other means. [Priority 1] | If color is used to convey information, those who cannot differentiate between certain colors (and those with devices that have non-color or non-visual displays) will not receive the information. |
Quick test: Is your page viewable and understandable in monochrome? |
Enable the document to be reformatted for the purpose of presentation in different media and on different output devices. |
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Guideline | Rationale | Techniques | |
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1. | Separate content and structure from the presentation of that content and structure. Always separate the content on your site (what you say), and the way you choose to structure that content (how you say it), from the way the content and structure are presented (how you want people to "see" it).[Priority 2] | When content is
tied to presentation, such as color-coding list items to distinguish
between them in some way, it is difficult to impossible to transform the
information into a different modality.
Example. Character spacing and non-letter characters cause problems for screen readers. |
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2. | Use elements and attributes appropriately. [Priority 2] | When elements and attributes are used inappropriately, such as using structural elements for presentation purposes (e.g., H1 to create large, bold face text on some location other than a heading), user agents that allow users to navigate through the structure will be unable to do so properly. Reformatting the page for other media and devices can also be difficult. |
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3. | Ensure that moving, blinking, scrolling, or auto-updating objects or pages may be paused or frozen. This is particularly important for objects that contain text. Note. Does not apply to instant redirection. [Priority 1] | Some people with cognitive limitations or visual disabilities are unable to read moving text quickly enough or at all. Movement can also cause such a distraction that the rest of the page becomes unreadable for people with cognitive disabilities. Screen readers are unable to read moving text. People with physical disabilities might not be able to move quickly or accurately enough to interact with moving objects. People with photosensitive epilepsy can have seizures triggered by flickering or flashing in the 4 to 59 hertz range with a peak sensitivity at 20hz. |
Note. Avoid BLINK and MARQUEE since they are proprietary elements. See E-1 |
4 | Ensure that text and graphics are perceivable and understandable when viewed without color. [Priority 1] | When forground and background colors are too close to the same hue, they may not provide sufficient contrast when viewed using monochrome displays or by people with different types of color blindness. |
Quick test: Is your page viewable and understandable in monochrome? |
5. | If you use a number of different languages on a page, make sure that any changes in language are clearly identified. [Priority 2] | This is a particular problem for braille translators, especially when multiple languages appear on the same page. |
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Ensure all elements on a page are operational in a device independent fashion. | |||
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Guideline | Rationale | Techniques | |
1. | Ensure
that pages using newer technology will fail gracefully if the technology
is not supported or is turned off. [Priority 1] To "fail gracefully" means that either a) alternatives to important presentations or functions on a page (that make use of new features) are provided or b) that the rest of the page is usable without a presentation or function that relies on a new feature. |
With each release of HTML new features have been added. In the recent past, new features have incorporated new technologies such as the ability to attach style sheets to a page or to embed scripts and applets in a page. Older browsers ignore new features and some users configure their browser not to make use of new features. These users often see nothing more than a blank page or an unreadable page when new features do not fail gracefully. |
See also E-5 - text-only pages. |
2. | Enable keyboard operation of all page elements. [Priority 1] This allows all manner of alternative interfaces to access and operate the elements. | Someone who is using the page without sight, with voice input, or with a keyboard (or input device other than a mouse) will have a difficult time navigating a page if keyboard shortcuts are not provided for objects on the page. Access to image maps is impossible for these users if alternatives are not provided. |
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3. | Provide interim solutions to facilitate operation via assistive technologies and older browsers. [Priority 2] | Older
browsers are unable to "Tab" to edit boxes, text
areas and lists of consecutive links, making it difficult to impossible
for users to access them. Users not operating in a graphical environment are disoriented by being transferred to a new window without warning. |
Until most users
are able to secure newer technologies that address these issues:
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Provide orientation and contextual cues to facilitate understanding of complex pages or elements. | |||
Guideline | Rationale | Techniques | |
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1. | For frames, provide sufficient information to determine the purpose of the frames and how they relate to each other. [Priority 1] | Users with blindness and low vision often access the screen with "tunnel vision" and are unable to get an overview understanding of the page. Complex intertwinings of frames may also be difficult for people with cognitive disabilities to use. |
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2. | Properly markup abbreviations and acronyms. [Priority 2] |
Unless expansions for abbreviations and acronyms are provided they may be indecipherable when spoken or brailled. |
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3. | Group controls, selections, and labels into semantic units. [Priority 2] | This provides contextual information about the relationship between controls, which is useful for all users. |
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4. | Ensure that tables (not used for layout) have necessary markup to be properly restructured or presented by accessible browsers and other user agents. [Priority 1] |
Many user agents restructure tables to present them. Without appropriate markup the tables will not make sense when restructured. Tables also present special problems to users of screen-readers. These guidelines benefit users that are accesing the table auditorally or viewing only a portion of the page at a time (users with blindness and low vision, or using an auto-pc, or devices with small displays) |
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5. | Create link phrases that strike a balance between being an accurate description of the link, even when read out of context while at the same time, not being too long. [Priority 3] | Otherwise people who use your site who are blind, or have difficulty seeing, or are using devices that do not have displays or very small displays will have difficulty. If they are moving from link to link, and a link phrase does not make sense, they will then have to stop and read the text around the link in order to discover what it means. |
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General | |||
Guideline | Rationale | Techniques | |
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1. | Use
only - elements or attributes in the HTML 2.0 (or higher) specification - style rules in a W3C CSS specification. [Priority 1] |
By avoiding elements that can only be interpreted by a specific browser type, your pages will be able to be accessed by more people across a larger number of hardware and software devices. | Use a "composit"
checker that can test for multiple HTML specifications simultaneouly
such as_______________ or Bobby [Priority 1].
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2 | Do not use non-html technologies to display text unless an an accessible version of the page(s) is provided as well. [Prioity 1] Needs some work since "non-html" could include CSS, applets and scripts which are covered elsewhere. | PDF and other page rendering technologies often create pages that cannot be viewed or navigated using standard web access tools. |
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3. | Elements that contain their own user interface should have accessibility built in. [Priority 2] | The accessibility of objects with their own interface is independent of the accessibility of the user agent. Accessibility must therefore be built into the objects or an alternative must be provided.. |
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4. | Ensure that there are accessible alternatives to information or functionality provided by active content such as scripts and applets. [Priority 1] | Many users can not run scripts or applets at all. The "fail gracefully" provisions would cover this situation. However, some users who can, but rely on assistive technology such as screen readers or special input devices may not be able to receive the information, or activate the functions that the content provides. |
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5. | If,
after all of your best efforts, any page is still not accessible then
you MUST provide a link to an alternative page that is:
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Some pages will
be unable to fail gracefully at this time either because the visual
components are too complex, or because assistive technologies or user
agents (browsers) are lacking a specific feature. Known instances when a text-only page will be needed (not a definitive list):
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