Success criterion: What WCAG 2.0 requires
For all non-text content that is used to convey information, text alternatives convey the same information.
Note: for multimedia, this means that two alternatives are provided:
- a transcript
- a text alternative that identifies the purpose or function of the multimedia
Understanding this Success Criterion
Key terms and important concepts
- text alternative
A text alternative
- serves the same function as the non-text content was intended to serve.
- communicates the same information as the non-text content was intended to convey.
- may contain structured content or metadata.
Note: text alternatives should be easily convertible to braille or speech, displayed in a larger font or different colors, fed to language translators or abstracting software, etc.
Intent of this success criterion
Ensure that critical information presented visually or auditorilly is also available in text. End-users who are unable to interpret graphs are @@how it differs from the others. e.g., "functional" and "specific sensory experience." How know when to apply this instead of "can be ignored?" Also will need to reference "explicitly associated." Although, that criterion applies to all...kind of a meta-criterion...how address?
Applicability: When does this Success Criterion Apply?
When non-text content contains information that is necessary to understanding or interacting with the content (@@too broad).
To determine the information conveyed by non-text content:
- consider the context in which the non-text element occurs;
- consider the non-text content both from
- the content provider’s point of view and
- from the user’s point of view.
[@@ need to draft: What does the content provider want people to learn from the non-text content? What does the user need to learn from the text alternative? Is it important for users to draw their own conclusions based on the content as well as understanding the specific point the content-provider wanted to make?]
Techniques to meet this Success Criterion
Technology-Independent techniques for this Success Criterion
[@@example of linking to general techniques instead of including in-line. These are examples of the type of content we could link to, it is not the final form....THESE ARE JUST EXAMPLES FOR DISCUSSION AND TO COMPARE WITH OTHER APPROACHES]
- Describing illustrations, diagrams, and maps
- Describing tables and charts
- Describing graphs
- Providing transcripts of multimedia
- Identifying the purpose of non-text content that conveys information
Technology-Specific Techniques for this Success Criterion
- How to provide text alternatives in HTML
- Writing long descriptions in HTML (longdesc attribute, element content) [@@see other attached document (html-techs.html) for example of what this might include. based discussion with Ben and the I18N topic index]
- Identifying the purpose of non-text content in HTML (alt attribute, element content)
- How to provide text alternatives in SVG
- Writing long descriptions in SVG (desc element) (@@again - JUST AN EXAMPLE - THE DOCUMENT THAT WE'RE LINKING TO NEEDS UPDATING AND OTHER REVISIONS)
- Identifying the purpose of non-text content in SVG (title element)
- How to provide text alternatives in SMIL
Advisory techniques: going beyond this Success Criterion
@@not sure what to recommend here
Benefits for People with Disabilities
- People who are blind, have low vision, have cognitive disabilities or have trouble reading text for any reason can have the text read aloud to them by assistive technology or otherwise transform the presentation of the text to meet their needs (e.g., change the font face, the text size, or the background and foreground colors).
- People who are deaf, are hard of hearing, or who are having trouble understanding audio information for any reason can read the text presentation or have it translated and presented as sign language by assistive technology.
- People who are deaf-blind can read the text in braille.
- Additionally, text alternatives support the ability to search for non-text content and to repurpose content in a variety of ways.
Examples of this Success Criterion
@@need to clean these up.
A photograph of an historic event adds to a news story
A photograph of two world leaders shaking hands accompanies a news story about an international summit meeting. The text alternative says, “President X of Country X shakes hands with Prime Minister Y of country Y."
A photograph of an historic event illustrates diplomacy
The same image of two world leaders shaking hands appears on a Web site discussing intricate diplomatic relationships. The first text alternative reads, “President X of country X shakes hands with Prime Minister Y of country Y on January 2, 2009.” An additional text alternative describes the room where the leaders are standing, the expressions on the leaders' faces, and identifies the other people in the room.
An audio recording of an historic event provides verbatim record
The Web page described in the previous example includes a link to an audio recording of the leaders' press conference. The page links to a text transcript of the press conference. The transcript includes a verbatim record of everything the speakers say. It identifies who is speaking as well as noting other significant sounds that are part of the recording, such as applause, laughter, questions from the audience, and so on.
A bar chart compares sales by month
A bar chart compares how many widgets were sold in June, July, and August. The short label says, "Figure one - Sales in June, July and August." The longer description identifies the type of chart, provides a high-level summary of the data comparable to that available from the chart, and provides the data in a table.
An animation demonstrates how a car engine works
There is no audio and the animation is part of a tutorial that describes how an engine works. All that is needed is a description of the image. From "How car engines work: Internal combustion@@link"
Note: Further discussion and examples are needed for real-time silent video such as webcams.