Accessibility principles

To ensure you meet the WCAG standard guidelines, are you following the four design principles?

Why it’s important

Perceivable, Operable, Understandable, Robust – POUR, is a way of approaching web accessibility by breaking it down into four main aspects. Information should be Perceivable, interfaces should be Operable, content should be Understandable, and the meaning of the content should be Robust to changes in the way it is accessed.

Perceivable

Perceivable is the use of one's senses to identify content and interface elements.

Many users will perceive a system primarily visually, whilst for others to perceive may be a matter of sound or touch.

New and emerging technologies may include sensory cues for smell and taste. Consider the following queries as examples of "perceivable" technology:

• An online application form contains many input fields. If the field labels are not readable, how can the form be completed?
• A chart describes the change in exchange rates over a period of time. If a user cannot see the chart, how can they understand the data?
• A training video narrates a process for completing a task. If the video is uncaptioned, how can a Deaf or Hard of Hearing user learn how to complete the task?
• Is all content fully usable when the screen is enlarged up to 300%?
• A website's contact information is in the footer. If the contrast is insufficient to distinguish between background and text, how can a low-vision or color-blind user contact the site owner?
• A kiosk requires users to touch the screen to access an interactive display. If the touch-screen controls are out of reach of the user, how can they interact with the display?

Operable

Operability is the successful use of controls, buttons, navigation and other interactive elements.

For many users, this means visually identifying an interface control then clicking, tapping or swiping.

For other users, using a keyboard or voice commands may be the only way they can control the interface. Consider the following for Operability:

• A navigation menu reveals a sub-menu of links when a user hovers over it with a mouse. If the menu doesn't expand when it receives focus, how can a keyboard user access the sub-menu?
• To access a websites social media links the user can only do so by clicking with their mouse. If the links don't receive keyboard focus, how can the keyboard user follow the links?
• A web application requires the user to take a photo to verify their identity. What happens if it flashes more than three times in any one second period and provokes a seizure in susceptible individuals?
• An online form permits a user to make multiple selections from a drop-down menu. If the user cannot press the Control key and click on the menu, how can they make more than one selection?

Understandable

Information and the operation of the user interface must be understandable.

Users should be able to comprehend the content as well as learn and remember how to operate the interface. Consider the following examples:

• A website's navigation has many links displayed in a different order from page to page. If the user has to relearn basic navigation for each page, how can they navigate through the website?
• A PDF registration form contains required email and phone number fields. If the user is not informed when there is an input error how can they understand why they can't submit the form?
• A Word document contains some non-English words and phrases. How can assistive technology present the text correctly if the languages are not indicated?
• A technical website makes use of many abbreviations, acronyms and jargon. If these are never defined, how can users understand the content?

Robust

Content must be robust enough to function on all appropriate technologies.

Users should be able to access content as technologies advance.

As technologies and user agents evolve, the content should remain accessible. The following examples are applicable:

• A website requires a specific version of a web browser to make use of its features. If a user doesn't or can't use that browser, how can that user experience the features of the site?
• A document format is inaccessible to a screen reader on a specific operating system. If a user employs that OS for day-to-day tasks, how can they gain access to the document?
• An online training video requires an inaccessible plug-in for the web browser. If the user can't play the video in an accessible way, how can they take part in the training?
• A web application doesn't include alternative inputs, such as keyboard or voice commands. Without alternative input methods, how can certain users use the application?