The Principle Explained
If you have ever poked around an attractive-looking website written in a language you do not recognize, you know that it is possible to explore a site without understanding a single word.
Principle 3 builds on the principles that come before it. Conforming to Principle 1 ensures that users can perceive a site. Conforming to Principle 2 ensures that users can act upon a site. But, even if visitors can see and interact with content, a site is not fully accessible if users cannot make sense of it. Principle 3 is about increasing the odds that visitors actually understand the content.
Even if content is written in your own language, it does not make the content understandable. For example, a page may contain:
- Unfamiliar words or abbreviations
- Overly complex instructions
- Messages that tell you that you made a mistake, but fail to explain how to fix it
- Interactive components that look familiar but behave in unpredictable ways
Barriers to understanding content are felt acutely by users with disabilities. Take, for example, the following scenarios:
- A student with low-vision uses magnification software. She needs to enlarge text so much that only a few words fit on the screen at one time. The lack of context makes it harder for her to understand abbreviations. Does “PC” mean personal computer, police constable, politically correct, or privy council?
- A professor with a learning disability is an expert in his field. He is very familiar with the jargon of the field, but he has trouble making sense of long and — from his perspective — unnecessarily complex sentences.
- An online job-application form indicates required fields in colour. Because screen readers only read text, an applicant who is blind is not able to determine which fields are required and which are optional.
By following Principle 3 guidelines, visitors will be better able to understand the content. Principle 3 is organized around three ideas. For web content to be understandable, these three items must be followed:
- People must be able to read it: The content is readable.
- The site must behave in ways that people can predict: The content is predictable.
- The site must be designed to help people avoid mistakes. When they do make mistakes, it should be forgiving of errors. In the language of WCAG 2.1, the site provides input assistance.