Info or functionality is unavailable at 320px width equivalent

Rule

Content MUST be presented without loss of information or functionality when the viewport is set to 320 pixel width equivalent.

Background

People with low vision often read content on a desktop computer by scaling content using the browser zoom - up to 400%. When zooming causes content to overlap other content, users with low vision may not be able to see or use that content. When content is created so that it reflows without losing information or functionality at screen widths down to 320px, users can view a web page in a 1280px width browser screen and zoom the content to 400% (320px) without having to scroll side to side to read and without losing access to content.

How to Fix

Fix this issue by ensuring all content and functionality are still available either: directly on the screen, revealed via accessible controls on the same screen, accessible via direct links from the screen being assessed, or via clear instructions on how to locate the content or functionality when content is set to a 320 pixel width equivalent.