Web Accessibility Principles

The information presented within this glossary entry is aimed at website owners seeking to learn the ropes of web accessibility. Technical elements are described in layman’s terms, and, as a rule, all topics pertaining to the legalities of web accessibility are presented in as simplified a manner as possible. This guide has no legal bearing, and cannot be relied on in the case of litigation.

The web accessibility principles are what the Web Content Accessibility Guidelines (WCAG) are based on. Created by the World Wide Web Consortium (W3C), WCAG is considered by many to be the most important set of guidelines impacting global web accessibility policy. Websites and web content that conform to these guidelines are generally considered accessible to people with disabilities. The current version of the Web Content Accessibility Guidelines (WCAG), WCAG 2.1, is organized around four guiding principles: Perceivable, operable, understandable, and robust. 

Here’s what each principle means:


Website visitors must be able to perceive the content and information that’s presented on your website using one or more of their senses (i.e., sight, sound, and touch).

Examples of perceivable problems:

  • A video appearing on a website with no closed captions or transcriptions
  • A PDF file that is not tagged correctly
  • A meaningful image (i.e., the kind conveying significant information) appearing without alternative (alt) text

Examples of perceivable solutions:

  • Text-based alternatives should be provided for any non-text content, such as closed captions and alt tags
  • Ensuring proper color contrast between text and its background
  • Correctly tagging PDF files and making them compatible with screen readers


Website visitors must be able to control a website's UI elements regardless of their physical condition. People who are blind, have epilepsy, motor disabilities, weak muscles, injured limbs, or cognitive limitations will need to be able to easily navigate through and use a website.

Examples of operable problems:

  • A website that can only be navigated and operated via a mouse
  • A form that is time-based and doesn’t provide enough time for people with cognitive disabilities to understand it

Examples of operable solution:

  • Ensuring a website is fully accessible via keyboard
  • Designing a website in a way that cannot potentially induce seizures by eliminating content that flashes more than three times per second


Website content should be presented in a simple, direct way. Website visitors shouldn't be misled or confused, including those with learning and attention disabilities.

Examples of understandable problems:

  • Not declaring a web page’s language in code which can lead screen readers to mispronounce words appearing within the page
  • Not clearly identifying errors on forms

Example of an understandable solution:

  • Ensuring the navigation menu appears consistently throughout the website


Websites should use clean HTML, CSS and Javascript code, written according to recognized standards. Just as importantly, websites should be compatible with the types of assistive technologies that a person with disabilities typically use, such as screen readers.

Example of a robust problem:

  • Status updates, such as ‘item added to cart’ on an eCommerce store, not being announced by screen readers

Example of a robust solution:

  • Correctly indicating ARIA live regions in code so that screen readers will announce changes 

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