Too Long; Didn't Read
The Web Content Accessibility Guidelines are a set of guidelines and recommendations for how to make your web content more accessible. Websites must be Perceivable, Operable, Understandable, and Robust (POUR) For a website to be robust, users must be able to use the site on a wide variety of devices, screen sizes, and browsers, including when used with assistive technology. The current version of this document at the time of this writing is WCAG 2.1. It's a very technical document, very long, and potentially exhausting to read.