Perceivable – Information and user interface components must be presentable to users in ways they can perceive
Operable – User interface components and navigation must be operable
Understandable – Information and the operation of user interface must be understandable
Robust – Content must be robust enough that it can be interpreted reliably by a wide variety of user agents, including assistive technologies
Consider perspectives
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Do accessibility and usability overlap?
Or are they less related?
Accessibility becomes usability
"Usability" criteria in WCAG
The following slides are excerpted from WCAG 2.0. They present, in no particular order, some guidance that is important for people with disabilities and is also good for mainstream usability.
Note wording has been simplified in a manner that changes some details meaning; reference the original for full information.
Color
Accommodate varied colour perception requirements and preferences.
1.4.1 Use of Color: Color is not used as the only visual means of conveying information
1.4.3 Contrast (Minimum) and 1.4.6 Contrast (Enhanced): The visual presentation of text and images of text has a contrast ratio of at least 4.5:1 or 7:1 respectively
Some people have visual perception issues that can be mitigated by using custom colours. Others have strong than average preferences for what facilitates their reading.
Customizability
Allow users to customize presentation, without destroying the usability of the content.
1.4.4 Resize text: Text can be resized without assistive technology up to 200 percent without loss of content or functionality
1.4.5 Images of Text: Text is used to convey information rather than images of text
1.4.8 Visual Presentation: Users can ensure text has custom color, is not too wide, is not justified, can increase line spacing, and can be resized
Allowing users to customize presentation maximises utility to them. Site design should accommodate this, not force users to accommodate the design.
Keyboard
Ensure users who do not use a pointing device have full functionality.
2.1.1 Keyboard and 2.1.3 Keyboard (No Exception): All functionality of the content is operable through a keyboard interface
2.1.2 No Keyboard Trap: The keyboard is not trapped in objects
2.4.3 Focus Order: Focusable components receive focus in an order that preserves meaning and operability
Many users with disabilities do not use a pointing device. Others access content in situations in which it is not convenient to use a mouse or is faster to use the keyboard to navigate.
Timing
Accommodate slower than expected interaction whenever possible.
2.2.1 Timing Adjustable: Users can turn off or extend time limits
2.2.5 Re-authenticating: When an authenticated session expires, the user can continue the activity without loss of data after re-authenticating
Some disabilities cause users to work more slowly, and users of assistive technologies may have to work more slowly as well. Situations such as distractions and interruptions can also cause users to slow down.
Distraction
Avoid features that distract users from the main content.
2.2.2 Pause, Stop, Hide: Users can stop moving, blinking, scrolling, or auto-updating information
2.2.4 Interruptions: Interruptions can be postponed or suppressed by the user
2.3.1 Three Flashes or Below Threshold and 2.3.2 Three Flashes: Web pages do not contain anything that flashes more than three times in any one second period
Some users are more inconvienced by distractions than others, and can find it difficult to find their place again. Included here is a requirement that users not be "distracted" by seizures related to photosensitive epilepsy.
Orientation in Site
Provide information to orient users within the site. It can be difficult to find the desired content otherwise.
2.4.2 Page Titled: Web pages have titles that describe topic or purpose
2.4.5 Multiple Ways: More than one way is available to locate a Web page within a set of Web pages
2.4.8 Location: Information about the user's location within a set of Web pages is available
3.2.3 Consistent Navigation: Navigational mechanisms occur in the same relative order each time they are repeated
3.2.4 Consistent Identification: Components that have the same functionality within a set of Web pages are identified consistently
A site structure that is obvious to the developer is not always obvious to the user. A variety of features help users get oriented and work with different styles.
Orientation in Page
Provide features to orient users within the page. Not all users "grok" the overall page design.
2.4.10 Section Headings: Section headings are used to organize the content
2.4.6 Headings and Labels: Headings and labels describe topic or purpose
2.4.7 Focus Visible: Keyboard focus indicator is visible
Users of assistive technology may only perceive the page in small chunks at a time, or in a linear fashion, and it is easy to get lost even within a given page, or hard to find the content of interest. The same applies to users on small devices such as mobile phones or who "skim" content.
Understandability
Support understanding of complex content.
3.1.3 Unusual Words: A mechanism is available for identifying specific definitions of idioms and jargon
3.1.5 Reading Level: Text does not require reading ability more advanced than the lower secondary education level
Assistive technology can need support to render unusual words in a meaningful way. Some disabilities directly relate to ability to understand certain types of content. In general, people have a wide variety of reasons given content may be difficult to understand, such as accessing in a non-native language, or even just woke up!
Surprises
Do not perform unexpected actions that cause users to get lost.
3.2.1 On Focus: When any component receives focus, it does not initiate a change of context
3.2.2 On Input: Changing the setting of any user interface component does not automatically cause a change of context unless the user has been advised of the behavior before using the component. (Level A)
With some assistive technologies, it can be difficult to find your place again if something moves focus unexpectedly. In general interruptions are distracting and disorienting.
Errors
Help users avoid and correct input errors.
3.3.1 Error Identification: Input errors are described to the user in text
3.3.3 Error Suggestion: Suggestions for correction of input errors are provided to the user
3.3.4 Error Prevention (Legal, Financial, Data) and 3.3.6 Error Prevention (All): User input is reversible or users are given opportunity to check it
Often, input errors can be automatically detected. It is important to provide meaningful support when this happens, rather than just tell users something was wrong.
Labels
Properly identify controls and provide additional help where appropriate.
3.3.2 Labels or Instructions: Labels or instructions are provided when content requires user input
3.3.5 Help: Context-sensitive help is available
Identifying controls helps users use them properly.
WCAG Conformance
WCAG 2 is general, broadly applicable guidelines
Conformance benefits many users, but doesn’t guarantee all unique needs are met
WCAG 2.0 is baseline guidance, suitable for policy adoption
Appropriate to go beyond WCAG 2.0 for certain audiences
User testing, including persons with disabilities, is recommended
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