Web Accessibility Principles
Overview
The four core principles of web accessibility come from the Web Content Accessibility Guidelines (WCAG), developed by the W3C. These principles—Perceivable, Operable, Understandable, and Robust—serve as the foundation for making digital content usable by people with disabilities. Known by the acronym POUR, they apply across websites, applications, and all forms of online content.
Perceivable
Users must be able to perceive all content, whether through sight, sound, or touch. Common issues include videos without captions or transcripts, images lacking alt text, and PDFs with no structure or tagging. Solutions include providing text equivalents for non-text elements, using proper color contrast, and structuring files to be screen reader–friendly.
Operable
Users must be able to interact with and navigate a site regardless of their physical abilities. Common issues include sites that require a mouse to navigate and time-limited interactions that can't be adjusted. Solutions include ensuring full keyboard accessibility and avoiding flashing content that may trigger seizures.
Understandable
Information and interface operations must be clear and predictable. Common issues include missing language declarations, inconsistent navigation, and vague form error messages. Solutions include clearly identifying form errors, making navigation consistent sitewide, and declaring language in HTML for screen readers.
Robust
Content must work reliably with current and future user agents, including assistive technology. Common issues include screen readers not announcing dynamic content. Solutions include using ARIA roles and properties such as aria-live and following semantic HTML and validated code practices.
Why It Matters
Following these principles ensures that websites remain accessible to the broadest audience. POUR supports compliance with laws like the ADA and Section 508, but more importantly, it enables equal access to digital content for users with disabilities.