Apple Ships Safari Technology Preview 243 with Major Accessibility Overhaul and CSS Improvements

Breaking: Safari Technology Preview 243 Released

Apple has released Safari Technology Preview 243, bringing critical fixes for VoiceOver users and significant CSS enhancements. The update is available immediately for macOS Tahoe and macOS Sequoia, with existing users able to update via System Settings under General → Software Update.

Apple Ships Safari Technology Preview 243 with Major Accessibility Overhaul and CSS Improvements — Source: webkit.org

This release addresses long-standing issues that impact assistive technology users, said a WebKit engineer. The fix for contextmenu events inside iframes is particularly important for keyboard-only navigation.

Accessibility Fixes

Multiple VoiceOver bugs have been squashed in this release. Developers and users relying on assistive technology will notice immediate improvements.

Contextmenu events in iframes: Previously, the contextmenu event was not fired for elements inside iframes when triggered by keyboard or VoiceOver actions (e.g., VO+Shift+M). This has been resolved. (310897@main, 164128676)
Color picker activation: VoiceOver’s press action now correctly activates color picker inputs. (311168@main, 172218114)
aria-hidden invalidation: Fixed invalidation of aria-hidden="true" when focus lands inside the subtree. (311648@main, 174449524)
Base <select> support: VoiceOver now properly supports base <select> elements, including closing the popover on selection and correct accessibility path positioning with CSS transforms. (311587@main, 175058883)

Animation Improvements

Two key animation bugs have been fixed, ensuring smoother transitions and transforms.

!important overrides: Fixed an issue where !important declarations did not override CSS animation values when CSS transitions ran on the same property. (310810@main, 174367827)
Transform animation accuracy: Identity matrix decomposition no longer generates invalid quaternions, preventing incorrect transform animations. (311267@main, 174813328)

CSS Updates

New features and critical bug fixes make this release essential for web developers.

New Features

contain: style for quotes: Added support for contain: style applying to CSS quote counters, as per CSS Containment Level 2. (311785@main, 84758186)
text-autospace insert keyword: Added support for the insert keyword in the text-autospace property. (311503@main, 175031507)

Resolved Issues

Flex layout: Now uses the used flex-basis instead of the specified value for definiteness evaluation. (311579@main, 85707621)
Anonymous block positioning: Fixed incorrect element positioning when containing block is an anonymous block. (311275@main, 96548847)
Box-shadow on table-row: box-shadow now works on display: table-row elements. (310609@main, 96914376)
text-indent with calc(): Percentage components in text-indent with calc() are correctly treated as zero for intrinsic size contributions. (310759@main, 97025949)
Out-of-flow height: Fixed incorrect height for out-of-flow content set to fit-content. (311375@main, 97492632)
Percentage size in flex items (quirks): Resolved percentage size resolution issues in flex items when in quirks mode. (311590@main, 100183902)
clip-path border-radius: clip-path: inset() border-radius values now render correctly at various element sizes. (310643@main, 110847266)
-webkit-box in fieldset: Emulated flexbox using -webkit-box now sizes children correctly inside <fieldset>. (311784@main, 114094538)
:where and :is performance: Improved performance on pages using :where and :is selectors. (311212@main, 114904007)
display: table with borders: Fixed incorrect layout when borders are present on display: table elements. (311276@main, 116110440)
aspect-ratio with border and absolute: Elements with border, position: absolute, and aspect-ratio: 1 now render as squares. (311267@main, specific fix included)

Background

Safari Technology Preview is a development-focused browser that allows web developers to test upcoming WebKit features. This version, Release 243, includes changes from WebKit builds 310600 to 312007. It is designed to provide early access to bug fixes and new specifications before they reach stable Safari releases.

The release is part of Apple's ongoing effort to improve web standards compliance and performance. Each build targets both macOS Tahoe and macOS Sequoia, ensuring compatibility across the latest operating systems.

What This Means

For developers, this update ensures better cross-browser compatibility and improved rendering accuracy. The accessibility fixes mean VoiceOver users will experience smoother interactions with web forms, select elements, and custom controls. The CSS enhancements reduce layout bugs, especially in flexbox and table rendering, which have long frustrated developers.

End users benefit from more predictable behavior when using assistive technology. The animation fixes also prevent visual glitches in transformed elements. As always, Apple urges developers to test their websites with the Technology Preview to catch issues early. The update is available now for download, and existing installations can be updated seamlessly through System Settings.

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