Safari Technology Preview 252 adds unprefixed user-select and named-feature() to CSS support

Safari Technology Preview 252 introduces two CSS features that reduce vendor prefixing. The unprefixed user-select property simplifies code that previously required -webkit-user-select, while the named-feature() function in @supports conditions enables more granular feature detection. These changes align Safari with other modern browsers, reducing cross-browser inconsistencies for engineers testing new CSS standards.

The release addresses several animation bugs that could cause visual glitches or performance issues. Fixed issues include incorrect frame rate alignment for new animations, misaligned timeline boundaries for sticky elements, and improper acceleration of width/height animations. These fixes improve the reliability of scroll-linked animations and view timelines, which are increasingly used in modern web applications.

Grid layout and line-clamp implementations receive multiple fixes, resolving issues like subgrid columns ignoring parent grid distribution, margins not contributing to intrinsic sizes, and unexpected ellipsis rendering. These changes affect responsive layouts and text truncation, where small rendering differences could break designs or accessibility features. Engineers can now expect more consistent behavior across Safari and other browsers.

Accessibility improvements focus on correct accessible name computation, particularly for display: contents elements and list markers. These fixes ensure screen readers interpret content structure accurately, which is critical for compliance with accessibility standards. The changes also prevent text duplication in accessible names, improving the user experience for assistive technology users.

The release is available for macOS Golden Gate and macOS Tahoe, with updates delivered through System Settings. Engineers testing new web features or debugging Safari-specific issues can use this preview to validate their code against upcoming WebKit changes. The fixes and additions reflect ongoing work to align Safari with evolving web standards, though some features may still require testing across other browsers.