Web Accessibility Initiative. (June 3, 2018). Web Content Accessibility Guidelines (WCAG) 2.1. W3C. Retrieved from https://www.w3.org/TR/WCAG21/
Web Accessibility Initiative. (June 3, 2018). Web Content Accessibility Guidelines (WCAG) 2.1. W3C. Retrieved from https://www.w3.org/TR/WCAG21/