U.S. Government Website Accessibility Guidelines
U.S. Government Website Accessibility Guidelines |
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| NASA Accessibility Guideline Checklist and Explanations | |||
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No. |
Web Practice |
Accessibility
Standard |
Explanation |
| 1. |
Text equivalent |
Every non-text element shall be provided via "alt" (alternative text attribute), "longdesc" (long description tag) or in element content. |
The "alt" text tag provides a title or descriptive phrase about the image it accompanies. This is essential for users of reader software who are vision impaired and it is valuable for users of graphical browsers who have "load images" turned off. It is also useful for users of text-only WWW tools like Lynx. The "longdesc" tag can be essential when an image conveys important information such as what about the image represents a discovery if the image is a science result image. |
| 2. |
Web page design |
All information conveyed with color must be available without color. Good primer on Color Blindness Link used with author's permission. |
Thirty percent of all males suffer from some form of color deficiency rendering colors as grays or spreading one color across several others. Choose text and background colors to provide maximum contrast. Contrast is also very important for individuals who can see but have reduced vision. Good design also refers to the ability of reader software to properly parse a page correctly left to right and up to down. |
| 3. |
Language identification |
Changes in natural language of document text and alt text equivalents must be clearly identified. |
The new HTML 4.x specification calls for identification of the language of the site or page using the "lang" tag. This has important implications for international sites and also when using style sheets. Correctly tagged web pages, when seen by browsers with appropriate ISO character sets installed will properly render specific language character sets including accents and special characters or entities. |
| 4. |
Organization |
Must be readable without requiring an associated style sheet |
Style sheets present a double-edged sword: Only the latest browsers support the specification and when using them the text still needs to be able to be parsed correctly by reader software. |
| 5. |
Dynamic content |
Web pages shall update equivalents when the dynamic content changes. |
Some scripts enable dynamic content to be generated based upon user input and server-side interaction (asp, cf, cgi, etc.). When the content changes for an image or a link or another object, the "alt" contents of the changed element should be included. This may be easier to accomplish for database-driven changes since "alt" tag information can be stored as well. This also applies to sites using frames. |
| 6. |
Server-side image maps |
Redundant text links shall be provided for each active region. |
Most sites have moved away from server-side image maps. The exception is for such things as geographical information system clickable maps. |
| 7. |
Client-side image maps |
Provide whenever possible in place of server-side image maps. |
Modern browsers support client-side image maps, with the addition of "alt" text tags for the image hot spots, assistive technology readers can provide additional clues. However, if the user has "load images" turned off, the only approach is to provide alternative links elsewhere on the same page. |
| 8. |
Data tables |
Provide information of row and column headers. |
Using row and column headers becomes crucial when a table is larger than two columns or two rows. Without the headers, assistive technology such as reader software can only recite the table contents with no reference to what that column or row pertains to. See below. |
| 9. |
Multi-logic row or column headers |
Provide markup to associate data cells and header cells for data tables. |
Additional information such as "summary" and "scope" can be applied to data tables to render their contents and intent meaningful to users of assistive technology. See above. |
| 10. |
Frames |
Must be titled with text that facilitates identification and navigation. |
Frames present unique obstacles to users of reader software. A frame-based page should always include an alternative layout (text only) inside a NOFRAMES element. Also, with the "title," "name" and "longdesc" tags, frames can be made more navigable for reader software. |
| 11. |
Page availability |
Must be usable when scripts, applets, or other programmatic objects are turned off or not supported, or provide equivalent information on an alternative page |
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| 12. |
Equivalent alternatives |
Must be synchronized with any multimedia presentation. |
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| 13. |
Content tracking |
Provide assistive technology users the option to skip navigation links with an appropriate method. |
There are a number of methods of facilitating navitation for users of assistive technology. Be consistent in page-to-page design, designers can provide a jump-link to bypass a series of links on a page similar to the "back to top" used in long pages, when using multiple links close together, separate the links so the reader software can parse it correctly. Links should be referenced with text which make sense if a user if link-jumping. Also, consider adding a site map, which is useful to nearly everyone. |
| Table 2-1 (taken from the U.S. Architectural and Transportation Barriers Compliance Board Recommendations) | |||
This document was assembled to assist NASA webmasters in the goal of making all Government websites accessible. Additional links and/or source material is invited. Please forward suggestions or corrections to Charles Redmond, NASA HQ Webmaster.