While working to educate yourself on web accessibility, you may have asked yourself these very questions.
The World Wide Web Consortium (W3c) is an international community that was established in 1994 to develop Web standards. They developed the Web Content Accessibility Guidelines (WCAG) as "a single shared standard for web content accessibility that meets the needs of individuals, organizations, and governments internationally." This standard is what is used to determine accessibility of websites today.
The guidelines are organized under four principles: perceivable, operable, understandable, and robust.
- 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)
The idea behind these principles is that if any of the things listed above are not true, users with disabilities will not be able to use the Web.
The WCAG (now 2.0), includes over 50 accessibility checks, but if you are looking for some quick and easy wins, we have a ten-point checklist that includes some of the most common accessibility errors.
When you are ready to go further, take a look at WebAIM's checklist. It is a more reader-friendly version of the official WCAG 2.0 standard.