Safari Technology Preview 243: Key Updates and Fixes Explained

Welcome to this Q&A breakdown of Safari Technology Preview 243, now available for download on macOS Tahoe and macOS Sequoia. This release brings a host of accessibility, animation, and CSS enhancements that refine the browsing experience and fix longstanding glitches. Below, we answer the most pressing questions about the update, covering everything from VoiceOver improvements to layout corrections. Use the links to jump directly to topics of interest.

What are the key accessibility improvements in Safari Technology Preview 243?

This release addresses several accessibility issues, making Safari more usable for people relying on assistive technologies. One major fix ensures that the contextmenu event now properly fires for elements inside iframes when triggered via keyboard or assistive actions like VoiceOver's VO+Shift+M. Previously, this event was missing, hindering custom context menus. Additionally, color picker inputs can now be activated using VoiceOver's press action, resolving a frustrating barrier. Another important improvement corrects the invalidation of aria-hidden="true" when focus moves inside an aria-hidden subtree—this ensures screen readers correctly ignore hidden content. Lastly, VoiceOver support for base <select> elements has been enhanced: the popover now closes upon selection, and the accessibility path positioning works correctly even when CSS transforms are applied. These fixes collectively make Safari more inclusive for users with disabilities.

Which animation issues were resolved in this release?

Two significant animation bugs have been squashed. First, a problem where !important declarations failed to override CSS animation values when CSS transitions were also running on the same property has been fixed. This ensures that developer-specified important rules take precedence as intended, preventing unexpected animation behavior. Second, an issue with identity matrix decomposition generating invalid quaternions has been corrected. This bug affected transform animations, causing incorrect rotations or scaling. Now, transform animations work accurately, providing smoother and more predictable visual effects. These fixes are especially valuable for web developers creating complex animations, as they eliminate subtle but impactful rendering errors.

What new CSS features were added?

Two notable CSS features debut in this release. First, support has been added for contain: style applying to CSS quote counters, as specified in the CSS Containment Level 2 specification. This allows developers to limit the scope of style containment, which can improve performance by telling the browser that certain style changes don't affect elements outside the contained subtree. Second, the insert keyword is now supported for the text-autospace property. text-autospace controls automatic spacing between characters, and the insert value inserts spacing only at specific points, offering more precise typographic control. These additions give web designers greater flexibility and performance optimization options.

What CSS layout and rendering bugs were fixed?

This update fixes a wide range of layout and rendering issues. Flex layout now uses the used flex-basis instead of the specified value for definiteness evaluation, aligning with the spec. An issue where element positioning was incorrect when the containing block was an anonymous block has been resolved. box-shadow now works on display: table-row elements, and text-indent with calc() containing percentages correctly treats percentage components as zero for intrinsic size contributions. Out-of-flow content with fit-content now has correct height, and percentage size resolution in flex items in quirks mode behaves as expected. Additionally, clip-path: inset() with border-radius values renders accurately at various sizes. The emulation of -webkit-box flexbox now sizes children correctly inside <fieldset> elements. Finally, elements with display: table and borders, and those with border, position: absolute, and aspect-ratio: 1 now render as squares. These fixes ensure more predictable and consistent layouts across different scenarios.

How does this release improve performance for CSS selectors?

Performance on pages using :where and :is selectors has been improved significantly. These modern CSS pseudo-classes are widely used for grouping selectors and reducing specificity. In previous versions, pages heavy with such selectors experienced slower style recalculations, especially on complex sites. The optimization in this release speeds up the matching process, making page rendering more efficient. Developers can now use these selectors more freely without worrying about performance penalties, leading to cleaner and more maintainable stylesheets while maintaining fast load times.

What should developers know about the fixed contextmenu event for iframes?

The fix for the contextmenu event inside iframes is particularly important for web applications that provide custom right-click menus. Previously, when using keyboard navigation or assistive technology (such as VoiceOver's VO+Shift+M) within an iframe, the event failed to fire. This meant users couldn't access those custom menus, breaking functionality for accessibility. The resolution ensures that the contextmenu event triggers correctly regardless of input method. Developers should test any custom context menus inside iframes to confirm they now work as expected. This change aligns Safari with other modern browsers and improves parity for assistive technology users.