When designing a web page, the term "accessibility" refers to providing support so everyone, including people with disabilities, can use your page. There are then many needs that have to be considered, including, for instance, the following:

• Vision limitations, varying from poor eyesight, through color vision problems, all the way up to total blindness
• Hearing limitations, which require some fallback method for hearing impaired users
• Mobility limitations, which may imply difficulty or impossibility of using the hands or controlling a mouse
• Cognitive limitations, which may complicate understanding the information shown on screen

There are many tools that can assist disabled users, such as screen zooming, speech recognition, screen readers, braille terminals, closed captioning, and more, but even those tools need some extra information in order to work properly. The Web Content Accessibility Guidelines (WCAG) are a set of guidelines, published by the Web Accessibility Initiative (WAI) of the World Wide Web Consortium (W3C). The current version, 2.1, available online at https://www.w3.org/TR/WCAG21/, is based on four principles, known as POUR as an acronym:

• Perceivable: Information and user interface components must be presentable to users in ways they can perceive
• Operable: User interface components and navigation must be operable
• Understandable: Information and the operation of user interface must be understandable
• Robust: Content must be robust enough that it can be interpreted by by a wide variety of user agents, including assistive technologies

These principles, quoted from the cited page, include guidelines for use of color, working with a keyboard, providing information for screen readers, having enough contrast, displaying errors, and more; sufficient and advisory techniques, that can help follow the guidelines; and success criteria, meaning testable conditions to be used for conformance testing. The latter criteria are also used to define three levels of conformance: A, the minimum; AA, medium, including all of A and AA success criteria, and AAA, the hardest to attain, fulfilling all existing criteria—but it is acknowledged that it may be impossible to achieve for some sites.

Trying to make sure that your web application follows all guidelines and applies all techniques is not easy, so we'll see how we can add some tools to React in order to make your task a bit easier.