Compound Text Stress in Responsive UI Components: Combining WCAG Text Spacing and Controlled Text Expansion

Responsive interfaces are expected to accommodate changes in text while preserving access to content and functionality. This study examines how controlled text expansion and WCAG 2.2 Success Criterion 1.4.12 text-spacing adjustments affect the layout of reusable responsive UI components, separately and in combination. Twenty component implementations were selected from four public design systems and rendered under 32 conditions each, yielding 640 browser renderings. Automated geometric screening and visual review identified three confirmed layout failures, affecting two implementations. All three occurred at 320 CSS px and only when text expansion and increased spacing were applied together. The experiment also recorded layout stress events that did not meet the criteria for confirmed failure. These descriptive findings illustrate how combined textual stress can reveal problems that separate tests may miss. The limited number of failures does not support a statistical estimate of an interaction effect or generalisation to other components.