What's New in Safari Technology Preview 239: Accessibility, CSS, and Core Improvements

Table of Contents

• Accessibility
• CSS
• Editing
• Forms
• MathML

Apple has released Safari Technology Preview 239, the latest iteration of its experimental browser, now available for download on macOS Tahoe and macOS Sequoia. If you already have the preview version installed, you can update it via System Settings → General → Software Update. This release includes WebKit changes from build 307619@main to 308417@main, delivering a wide range of bug fixes and a few feature additions. Below is a detailed look at what’s new and improved.

Accessibility

The accessibility team has tackled several VoiceOver issues, making Safari more inclusive for users who rely on screen readers.

Resolved Issues

• SVG and unnamed images: Fixed an issue where SVG <use> elements referencing <symbol> inside an <img> were incorrectly treated as unnamed images in VoiceOver’s Images web rotor. (308126@main)
• Aria-owned rows in grids: VoiceOver could no longer access aria-owned rows and their cells within grids or tables—this has been resolved. (308087@main)
• Focusable splitter elements: Earlier, when navigating to the next or previous form control, VoiceOver missed focusable splitter elements. That gap is now closed. (308089@main)
• Aria-labelledby geometry: Controls using aria-labelledby now respect the native label’s geometry, even when both the control and its ARIA label lack a visible bounding box. (307727@main)

CSS

CSS receives a notable new feature along with several important bug fixes that enhance layout accuracy.

New Feature

• :open pseudo-class for inputs: Added support for the :open pseudo-class, allowing developers to style <input> elements based on their open state (e.g., when a date picker is expanded). (308148@main)

Resolved Issues

• Collapsed table borders: Tables with collapsed borders no longer spill extra border width into the margin area, because the first row’s width calculation is now correct. (308311@main)
• Inset box-shadow on table cells: Fixed incorrect positioning of inset box-shadow on table cells with collapsed borders. (307661@main)
• Subgrid intrinsic sizes: A subgrid (display: grid subgrids) inside grid-lanes containers no longer mistakenly contributes its child elements’ intrinsic sizes to the parent track sizing algorithm. (308253@main)
• Baseline calculation for inline-block: The baseline of inline-block elements now correctly falls to the bottom margin edge when overflow is not visible. (307718@main)
• Replaced element constraints: Replaced elements (like images and videos) now correctly apply min-height and min-width constraints in all configurations. (308212@main)
• Percentage heights in absolutely positioned elements: Children with percentage heights inside absolutely positioned containers using intrinsic height values (fit-content, min-content, max-content) now resolve correctly as auto instead of using the containing block’s height. (308226@main)

Editing

Two editing bugs have been squashed, improving the content creation experience.

Resolved Issues

• FormatBlock and inline styles: Executing execCommand('FormatBlock') previously discarded the inline styles of replaced block elements, causing text formatting to vanish when pasting content. This is now preserved. (308365@main)
• Text-indent flickering: The text-indent property no longer flickers or is ignored when typing inside contenteditable elements. (307646@main)

Forms

A single but critical forms bug has been fixed.

Resolved Issues

• Readonly date input: A readonly date <input> could still be edited via keyboard through the date picker—that loophole is now closed. (307934@main)

MathML

MathML rendering receives improvements for dynamic content and positioning.

Resolved Issues

• Attribute changes on <mo>: Dynamic changes to attributes of the <mo> element now trigger a relayout, ensuring math operators stay in sync. (308014@main)
• Positioning of <mpresc: The positioning of the <mprescripts> element (a placeholder for scripts in MathML) has been corrected. (Further details pending from WebKit.)

Safari Technology Preview 239 continues Apple’s commitment to refining the web platform, with a strong focus on accessibility, layout precision, and editing reliability. Developers and early adopters can download the update today and test these changes in their own projects.