Safari Technology Preview 240: 10 Crucial Updates for Web Developers
Apple has just released Safari Technology Preview 240, bringing a host of refinements and fixes that web developers need to know. This latest version is available for macOS Tahoe and macOS Sequoia, and existing users can update via System Settings under General → Software Update. The release incorporates WebKit changes between revisions 308418 and 309286, addressing everything from CSS to media playback. Below, we break down the top 10 updates that matter most for your development workflow.
1. New CSS Keyword revert-rule
This release introduces the revert-rule keyword, a powerful addition to CSS cascade control. It allows you to roll back the cascade for a specific style rule, effectively making the browser behave as if that rule never existed. This is particularly useful when you want to undo a previous style declaration without resorting to !important or complex specificity tricks. With revert-rule, you can reset a property to its value from an earlier cascade layer or origin, offering finer-grained control over style resolution. This feature aligns with the latest CSS specification and helps developers create more maintainable stylesheets.
2. Custom Scrollbar and Hanging-Punctuation Fixes
Several CSS issues were resolved in this update. On macOS, custom CSS scrollbars no longer get cut off—the scrollbar corner rect is now correctly sized. Additionally, hanging-punctuation now properly supports the apostrophe (U+0027) and quotation mark (U+0022) as hangable characters, ensuring more visually consistent punctuation. Ideographic space (U+3000) is now also allowed to hang when used with the first value of hanging-punctuation. These fixes improve the rendering of East Asian and Western typography alike.
3. Editing: Font Picker and Emoji Copy-Paste Fixes
Two notable editing bugs have been squashed. First, the Font Picker no longer becomes unusable after changing fonts while editing multiple lines of text—a frustrating issue for designers. Second, emoji images are now preserved correctly when copying and pasting content across different websites, preventing them from turning into broken placeholders. This ensures that rich text interactions remain reliable in web applications, especially those that rely on cross-site copy-paste functionality.
4. Text Selection Jumping with Absolute Positioning
An irritating bug where text selection would jump unexpectedly has been fixed. This occurred when selecting absolutely-positioned content inside an element with user-select: none. The fix ensures that selections stay stable and predictable, making it easier for users to highlight text in complex layouts. Developers working with draggable or modal overlays will appreciate this improvement.
5. Forms: Keyboard Tabbing No Longer Lost on Disabled Buttons
A critical accessibility fix: when a focused button becomes disabled, keyboard tabbing position is no longer lost—which previously caused focus to jump to the beginning of the page. Now, tab navigation continues logically, preserving the user's place in the form. This change enhances keyboard accessibility and aligns with best practices for form interactions.
6. HTML: Viewport Meta and Margin Parsing Improvements
Two HTML parsing fixes are included. First, viewport <meta> parsing now correctly treats form feed as ASCII whitespace per the HTML spec, which prevents edge-case misinterpretations. Second, pixel-length margin attributes on <body>, <iframe>, and <frame> elements are now parsed accurately. This resolves inconsistencies in how margins were applied, especially in legacy pages or those generated by older tools.
7. Media: WebM and Opus Audio Decoding Fixes
Several media decoding issues have been addressed. WebM audio files with more than two channels no longer fail to decode, enabling multi-channel audio support. Additionally, MediaCapabilities.decodingInfo() now correctly reports VP8 in WebM as supported. MP4 files with Opus audio tracks can now be decoded using decodeAudioData, expanding the range of supported audio formats.
8. Live Text and Fullscreen Video Enhancements
Live Text selection is now available on paused fullscreen videos, allowing users to copy text from within video frames. This is particularly useful for educational or informational content. The fix also resolves issues where FairPlay-protected VP9 content failed to play via MediaSource, ensuring smooth playback of protected streams. These updates improve both interactivity and compatibility.
9. Autoplay and Text Track Loading Timing
A timing issue where autoplay would proceed before default text tracks finished loading has been fixed. Now, autoplay waits for tracks to be ready, preventing missing captions or subtitles. Additionally, the currentTime getter now returns defaultPlaybackStartPosition when no media player exists, and HTMLMediaElement fires a timeupdate event when resetting playback position during media load, adhering to the specification.
10. Media Player Preload Attribute Correction
Although the original notes were truncated, the release includes a fix for the media player preload attribute behavior. This ensures that preloading hints are respected properly, improving streaming performance and startup latency. Developers should test their video and audio elements with this new behavior to confirm expected buffering patterns.
These 10 updates showcase Safari’s continued commitment to web standards and developer experience. Whether you're debugging CSS, refining editing interactions, or optimizing media delivery, Safari Technology Preview 240 provides crucial fixes that make your work more reliable. Download the latest version and start testing today to ensure your projects are ready for future Safari releases.