The document must not use the user-scalable="no" parameter in the element because it disables text scaling and zooming which is essential to users with low vision.
The user-scalable="no" parameter inside the content attribute of element disables zooming on a page. The maximum-scale parameter limits the amount the user can zoom. This is problematic for people with low vision who rely on screen magnifiers to properly see the contents of a web page.
Users with partial vision and low vision often choose to enlarge the fonts on their browser to make text on the web easier to read. The browser's viewport focus is everything visible in the browser window at a given moment. If the user maximizes the browser to full size on a high-resolution monitor, the viewport focus area is large and may include the entire web page.
If the browser window is small, the viewport focus area includes only a small part of the web page. The browser's viewport focus does not affect the programmatic focus. Users can scroll up and down the web page, but the programmatic focus does not follow the viewport. The Web Content Accessibility Guidelines calls for developers to design pages so that they support resize up to 200%; however, it is a best practice to require 5x zoom.