Principles of Accessibility: Principle 1 - Perceivable
Defining WCAG 2.0 Level AA Guidelines
Perceivable: Information and user interface components must be presentable to users in ways they can perceive.
Guideline 1.1 - Text Alternatives
1.1.1 - Non-text Content [A]
All non-text content that is presented to the user has a text alternative that serves the equivalent purpose.
Guideline 1.2 - Time-based Media
1.2.1 - Audio-only and Video-only (Prerecorded) [A]
For prerecorded audio-only and prerecorded video-only media, the following are true, except when the audio or video is a media alternative for text and is clearly labeled as such:
- Prerecorded Audio-only: An alternative for time-based media is provided that presents equivalent information for prerecorded audio-only content.
- Prerecorded Video-only: Either an alternative for time-based media or an audio track is provided that presents equivalent information for prerecorded video-only content.
- 1.2.2 - Captions (Prerecorded) [A]
Captions are provided for all prerecorded audio content in synchronized media, except when the media is a media alternative for text and is clearly labeled as such.
- 1.2.3 - Audio Description or Media Alternative (Prerecorded) [A]
An alternative for time-based media or audio description of the prerecorded video content is provided for synchronized media, except when the media is a media alternative for text and is clearly labeled as such.
- 1.2.4 - Captions (Live) [AA]
Captions are provided for all live audio content in synchronized media.
- 1.2.5 - Audio Description (Prerecorded) [AA]
Audio description is provided for all prerecorded video content in synchronized media.
Guideline 1.3 - Adaptable
Create content that can be presented in different ways (for example simpler layout) without losing information or structure.
- 1.3.1 - Information and Relationships [A]
Information, structure, and relationships conveyed through presentation can be programmatically determined or are available in text.
- 1.3.2 - Meaningful Sequence [A]
When the sequence in which content is presented affects its meaning, a correct reading sequence can be programmatically determined.
- 1.3.3 - Sensory Characteristics [A]
Instructions provided for understanding and operating content do not rely solely on sensory characteristics of components such as shape, size, visual location, orientation, or sound.
Guideline 1.4 - Distinguishable
Make it easier for users to see and hear content including separating foreground from background.
- 1.4.1 - Use of Color [A]
Color is not used as the only visual means of conveying information, indicating an action, prompting a response, or distinguishing a visual element.
- 1.4.2 - Audio Control [A]
If any audio on a Web page plays automatically for more than 3 seconds, either a mechanism is available to pause or stop the audio, or a mechanism is available to control audio volume independently from the overall system volume level.
- 1.4.3 - Contrast (Minimum) [AA]
The visual presentation of text and images of text has a contrast ratio of at least 4.5:1.
- 1.4.4 - Resize text [AA]
Except for captions and images of text, text can be resized without assistive technology up to 200 percent without loss of content or functionality.
- 1.4.5 - Images of Text [AA]
If the technologies being used can achieve the visual presentation, text is used to convey information rather than images of text.