WCAG Perceivable Success Criteria

Principle 1: Perceivable Guidelines

WCAG Perceivable Success Criteria
Information and user interface components must be presentable to users in ways they can perceive. This means that users must be able to perceive the information being presented. User agents, like screen readers, require clearly defined HTML elements within a structured web page. The ARIA (Accessibility Rich Internet Application) Landmarks and a hierarchy of Headers should be used to define page regions and content context. The Banner, Navigation panel, Main section, and Footer are visually perceivable on a standard computer screen, but not necessarily on a screen reader device.

Guideline 1.1 Text Alternatives

The intent of this Success Criterion is to make information conveyed by non-text content, such as images, accessible through the use of a text alternative. Text alternatives are a primary way for making information accessible because they can be rendered through any sensory modality (for example, visual, auditory or tactile) to match the needs of the user. That is, a person who cannot see a picture can have the text alternative read aloud using synthesized speech. A person who cannot hear an audio file can have the text alternative displayed so that he or she can read it.

Guideline 1.2 Time-based Media

The intent of this Success Criterion is to make information conveyed by prerecorded audio-only and prerecorded video-only content available to all users. An example of pre-recorded video with no audio information or user interaction is a silent movie. The purpose of the transcript is to provide an equivalent to what is presented visually. For prerecorded video content, authors have the option to provide an audio track. The purpose of the audio alternative is to be an equivalent to the video. This makes it possible for users with and without vision impairment to review content simultaneously. The approach can also make it easier for those with cognitive, language and learning disabilities to understand the content because it would provide parallel presentation.

Guideline 1.3 Adaptable

Create content that can be presented in different ways (for example simpler layout) without losing information or structure. The intent of this Success Criterion is to ensure that information and relationships that are implied by visual or auditory formatting are preserved when the presentation format changes. Sighted users perceive structure and relationships through various visual cues — headings are often in a larger, bold font separated from paragraphs by blank lines; list items are preceded by a bullet and perhaps indented; paragraphs are separated by a blank line; items that share a common characteristic are organized into tabular rows and columns; form fields may be positioned as groups that share text labels; a different background colour may be used to indicate that several items are related to each other; words that have special status are indicated by changing the font family and /or bolding, italicizing, or underlining them; items that share a common characteristic are organized into a table where the relationship of cells sharing the same row or column and the relationship of each cell to its row and/or column header are necessary for understanding; and so on. Having these structures and these relationships programmatically determined or available in text ensures that information important for comprehension will be perceivable to all.

Guideline 1.4 Distinguishable

Make it easier for users to see and hear content. The intent of this Success Criterion is to ensure that all users can access information that is conveyed by colour differences. If the information is conveyed through colour differences in an image (or other non-text format), the colour may not be seen by users with colour deficiencies. In this case, providing the information conveyed with colour through another visual means ensures users who cannot see colour can still perceive the information. Playing audio automatically when landing on a page may affect a screen reader user’s ability to find the mechanism to stop it because they navigate by listening and automatically started sounds might interfere with that navigation. Individuals who use screen reading software can find it hard to hear the speech output if there is other audio playing at the same time. Therefore, it is important that the user be able to turn off the background sound or control the volume level. Also, the intent of this Success Criterion is to provide enough contrast between text and its background so that it can be read by people with moderately low vision (who do not use contrast-enhancing assistive technology). It is important that colour is not a key factor so that people who have a colour vision deficit will also have adequate contrast between the text and the background.