POUR Principles of Web Accessibility
The POUR Principles of accessibility: Perceivable, Operable, Understandable and Robust form the foundation of the Web Accessibility Guidelines (WCAG) 2.0.
Perceivable
As a minimum requirement for accessibility people need to be able to perceive – that is see, hear or touch web content. Information that cannot reach the brain is inaccessible. There are four guidelines under this principle:
- Text alternatives – known as ‘alt’ text. All non-text content such as images must be provided with alt text. This text can be converted into different formats such as audio or Braille as required. The alt text should be meaningful, descriptive and reflect the purpose of the image. If the image does not convey meaning and is purely for decoration, you can specify an empty or null text for screen readers to avoid unnecessary clutter.
- Time based media - Time based means it runs over time like audio or video, rather than static content such as images and text. Audio content requires an alternative description for users with hearing impairments. This could be in the form of captions synchronized with the media. Video content that contains more than just dialogue, such as an action sequence would need an alternative text transcript or audio description so those with visual impairments can understand and make sense of the change in events. A text transcript is the minimum required for multimedia content to be made accessible.
- Adaptable – People with disabilities often need to change the way the information is presented to them, so it is easier to perceive and understand. E.g A dyslexic user may want to have the page read out to them via text or might want to change the colours and text size so that it is easier to read and understand. Web pages should be coded semantically using headers, lists and paragraphs to add a logical, non-visual structure to the page.
- Distinguishable – It’s important not to rely on colour alone to convey information. For instance, don’t rely on colour as the only way to distinguish segments in a pie chart, don’t start audio or video on a page automatically unless you provide a way of turning it off. Screen reader users may find it difficult to hear the speech output of their software if audio or video is playing at the same time.
Operable
Users should be able to find, navigate through and interact with web content such as forms and menus using a range of input methods and assistive technologies. There are four guidelines under this principle:
- Keyboard Accessible - Some people with mobility impairments and some people who use screen readers only use a keyboard to navigate a website. Keyboard users typically tab through a web page to interact with links, jump to the next question on a form and interaction with other controls. Websites that are not accessible with a keyboard only results in users getting stuck at a particular point on the site and cannot navigate back or forward. They then have to close the page and start again, this is very frustrating. This is often found with flash content such as a media player.
- Enough time - Some users will require longer than others to perform tasks on a website so it is important to give users enough time or adjust the flexibility of time required for tasks. For example, extending or doubling the duration of timeout.Content that moves or auto updates can cause problems for those who read stationary text slowly, or anyone who has trouble tracking moving objects. Blinking or scrolling content that lasts longer than five seconds should include the ability to pause, stop or be hidden by the user.
- Seizures - It is important that websites do not contain any features that flash or flicker more frequently than 3 times a second to avoid the risk of causing seizures for those with photosensitive epilepsy. PEAT, an online photosensitive epilepsy analysis tool can be used to test flashing or content that flickers.
- Navigable – Users should be able to easily navigate around a web page. Users should also be able to bypass or skip large blocks of content with the help of skip links. The focus order of links as you tab through a page should be logical and not jump around the page. Visual should be used to identify the current tab position. Screen readers often have problems with hyperlinks that do not make sense by them selves. At a minimum it should be possible to work out from the context of the link where it will take you. There for avoid using link phrases such as ‘click here’ or ‘more’, instead make them more descriptive.
Understandable
All web content should make sense and its behavior should be predictable. In addition any feedback provided about errors should be clear and helpful. There are three guidelines under this principle:
- Readable – Ensure the site is readable and understood and ensure it is coded using the right HTML language, such as English, French or Spanish. The language can be set for the whole page or part of a page, for example when a quote is used from another language. Screen Readers rely on the correct code language being used so they can use the correct speech engine to read out.
- Predictable – Ensuring pages are predictable helps users with visual disabilities, cognitive and motor impairments. When navigating through web pages it reduces the chance that a change of context will occur unexpectedly and cause confusion. Ensure elements are in the same place on each page and place elements where users would expect to see them – for instance your logo should be top left on every page and the search top right. Don’t allow changes to happen when tabbing of focusing on elements such as submitting data on a form submit button when the user tabs onto the submit button. Another example is when a form refreshes without warning. This is confusing for a screen reader user as they are sent back to the start of the page. Warning users of change will mean they will be less disorientated.
- Input Assistance – People with disabilities may be more likely to make mistakes when inputting information and at the same time it can be harder for them to detect an error. It is important to provide accessible input assistance such as error messages to avoid and then help them correct mistakes. Form errors, ideally should be marked with strong red text and ideally a hazard or warning symbol. Form fields should provide clear labels, cues and instructions providing enough guidance so users know what to do. If mistakes are made provide clear, helpful instruction on how to correct them as the nature of the error may not be obvious to people with visual or learning disabilities.
Robust
People use different operating systems, browsers and versions of browsers yet despite these different technologies they call expect the web to work. There is one guideline to this principle:
- Compatible – To maximize compatibility use good quality code that adheres to web standards such as the WC3, HTML and XHTML standards. Ensure that the code is checked against validation tools, errors are fixed and ensure multimedia movies such as Flash have descriptive labels associated with them.
Kept in: Accessibility, Anything web
