I've previously helped organisations ensure that a quick response (QR) code is visible on screen from an accessibility perspective. For example, a screen reader user may have only a small portion of the browser window visible on screen and a visually impaired user may have zoomed 400% (which breaks some of the designs I've seen, rendering the QR-code outside the viewport).
Someone who is visually impaired must feel confident that the full code they are being asked to scan is within the visible area.
My solution has previously been to utilise viewport size units (vh and vw), but this has had the limitation of not working well with headers and footers. These new viewport units appear to solve this problem! 👏🎉