2. Introduction to WCAG
WCAG Principles
The four guiding principles of WCAG say that web content must be Perceivable, Operable, Understandable, and Robust (POUR) in order to be accessible to people with disabilities.
- Perceivable – 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 (it can’t be invisible to all of their senses)
- Operable – User interface components and navigation must be operable.
- This means that users must be able to operate the interface (the interface cannot require interaction that a user cannot perform)
- Understandable – Information and the operation of user interface must be understandable.
- This means that users must be able to understand the information as well as the operation of the user interface (the content or operation cannot be beyond their understanding)
- Robust – Content must be robust enough that it can be interpreted reliably by a wide variety of user agents, including assistive technologies.
- This means that users must be able to access the content as technologies advance (as technologies and user agents evolve, the content should remain accessible)
Source: Introduction to Understanding WCAG 2.0
Perceivable
For content to be perceivable it must be possible to perceive it through multiple senses. While there are a variety of ways to provide alternatives perceivable through alternate senses (e.g., audio descriptions for visual content for those who are blind, or sign language interpretation of audio content for those who are Deaf), text alternatives are generally the best choice.
Text can be converted into a variety of forms. It can be read aloud by screen reading software or converted to braille for those who are blind. It can be translated into other languages for those reading in a second language or it can be magnified without losing its sharp appearance for those with low vision. Its colour can be changed easily to make it more readable for those who are colour blind, or need high contrast.
Operable
In the context of web accessibility, operability generally means that something is functional using a keyboard. If functional items are not keyboard operable, they will be inaccessible to many users.
Developers often create features that operate with a mouse, sometimes overlooking keyboard functionality. Most people accessing the Internet do use a mouse, but many do not. A person who is blind is unlikely to use a mouse, but will instead rely almost exclusively on keyboard access. Power users, often developers or programmers, also tend to be keyboard users, so usability is lost for this group as well when keyboard access is not programmed in.
Operable can also mean functional using one’s voice. Some people with severe motor impairments use voice recognition software along with switches (see figure below) to operate their computers and navigate the Web. This means there must be te