Safari Technology Preview 243: Key Updates and Fixes Explained

Welcome to our detailed Q&A breakdown of Safari Technology Preview Release 243. This update, available for macOS Tahoe and macOS Sequoia, brings a host of improvements across accessibility, animations, and CSS. Whether you're a web developer or an early adopter, these changes refine how websites and apps behave in Apple's preview browser. Below, we answer the most pressing questions about what's fixed, what's new, and how it impacts your workflow.

1. What accessibility issues were resolved in Safari Technology Preview 243?

This release tackles several accessibility bugs to improve support for assistive technologies. Key fixes include:

• Context menu in iframes: Previously, pressing keyboard shortcuts or using VoiceOver (VO+Shift+M) wouldn't trigger the contextmenu event inside iframes. This is now resolved. (Internal reference: 310897@main, bug 164128676)
• Color picker activation: VoiceOver users can now activate color picker inputs using the press action. (311168@main, bug 172218114)
• ARIA hidden invalidation: When focus lands inside a subtree marked with aria-hidden="true", that property is now properly invalidated. (311648@main, bug 174449524)
• Base select element support: VoiceOver now correctly closes popovers after selection and adjusts accessibility path positioning when CSS transforms are applied. (311587@main, bug 175058883)

These changes ensure a more seamless experience for users relying on screen readers and keyboard navigation.

2. What animation-related bugs were fixed in this release?

Two important animation issues were addressed:

• !important vs. CSS animations: When both CSS animations and transitions targeted the same property, !important declarations are now correctly honored, overriding the animation value. (310810@main, bug 174367827)
• Transform animation glitches: A bug in identity matrix decomposition was generating invalid quaternions, leading to incorrect transform animations—such as rotations appearing distorted. This fix ensures smoother, mathematically accurate transforms. (311267@main, bug 174813328)

These improvements stabilize motion effects, making them behave as intended in complex UI scenarios.

3. What new CSS features were introduced in Safari Technology Preview 243?

Two enhancements align Safari with CSS specifications:

• contain: style for quote counters: As defined in CSS Containment Level 2, the contain: style property now influences CSS quote counters (e.g., generated via content: counter(...)). This allows developers to limit style containment effects accurately. (311785@main, bug 84758186)
• text-autospace property: A new insert keyword has been added to the text-autospace property, giving more control over spacing behavior in text. (311503@main, bug 175031507)

These additions expand design possibilities while maintaining compatibility with modern CSS specs.

4. Which significant CSS bugs were resolved in this release?

Dozens of CSS corrections were applied. Here are some highlights:

• Flex layout fix: The engine now uses the used flex-basis value for definiteness evaluation, rather than the specified value. (311579@main, bug 85707621)
• Anonymous block containers: Element positioning is now correct when the containing block is an anonymous block. (311275@main, bug 96548847)
• Box-shadow on table-row: box-shadow now works properly on elements with display: table-row. (310609@main, bug 96914376)
• text-indent with calc(): Percentage components in calc() values for text-indent are treated as zero for intrinsic size contributions, matching spec. (310759@main, bug 97025949)
• Out-of-flow height: Elements with fit-content now calculate height correctly when out of flow. (311375@main, bug 97492632)
• Percentage sizes in flex items: Fixed percentage size resolution in flex items under quirks mode. (311590@main, bug 100183902)
• clip-path inset border-radius: clip-path: inset() now renders border-radius values accurately at various sizes. (310643@main, bug 110847266)
• -webkit-box in fieldset: Emulated flexbox via -webkit-box now correctly sizes children inside <fieldset> elements. (311784@main, bug 114094538)
• Performance boost: Pages using :where and :is selectors see improved performance. (311212@main, bug 114904007)
• Table with borders: Layout for display: table elements is correct when borders are present. (311276@main, bug 116110440)
• Square elements with aspect-ratio: Elements with border, position: absolute, and aspect-ratio: 1 now render as perfect squares. (no bug reference)

5. How do I install or update to Safari Technology Preview 243?

If you're running macOS Tahoe or macOS Sequoia, you can download the latest version directly from Apple's developer portal. For existing users, open System Settings → General → Software Update and check for updates. The build includes WebKit changes from revision 310600 to 312007, so ensure your system meets the minimum requirements. Keep in mind that this is a preview release—ideal for testing upcoming WebKit features, but not recommended for daily browsing without backups.

6. What is the WebKit change range for this release?

Release 243 incorporates commits from WebKit revision 310600@main to 312007@main. This spans several weeks of development, bringing over a thousand changes focused on stability, spec compliance, and performance. Key areas include accessibility fixes, animation corrections, and extensive CSS enhancements. Developers can browse the full history on the WebKit repository to see specific diffs.