Safari Technology Preview 240: Key Updates and Bug Fixes Explained
Welcome to the latest Safari Technology Preview release! Version 240 brings a suite of improvements and bug fixes for developers and early adopters. This update is available for macOS Tahoe and macOS Sequoia, and includes WebKit changes from revision 308418 to 309286. Below, we answer the most common questions about what's new, what's fixed, and how you can get the build.
1. How do I download or update to Safari Technology Preview 240?
If you're new to Safari Technology Preview, head to the official Apple Developer website to download the installer for macOS Tahoe or macOS Sequoia. Already have it installed? Updating is simple: open System Settings, go to General → Software Update, and the latest version will appear. The process is seamless, ensuring you stay on the cutting edge of WebKit development.
2. What new CSS feature does Safari 240 introduce?
The star of the show is the revert-rule CSS keyword, implemented in WebKit revision 308733. This keyword lets you roll back the cascade to behave as if the current style rule never existed. In practical terms, it provides a way to reset a property to its inherited or initial value without manually overriding each declaration. This is especially useful in component-based designs where you want to undo a previous rule while keeping other styles intact. Developers will find this a powerful addition for maintaining clean, predictable stylesheets.
3. What CSS bugs were fixed in this release?
Two important fixes address scrollbar and punctuation behavior. Custom CSS scrollbars on macOS sometimes appeared cut off or had incorrectly sized corner rectangles; that's now resolved (revision 309119). Additionally, the hanging-punctuation property now properly supports U+0027 (apostrophe) and U+0022 (quotation mark) as hangable quotes (revision 308597). A second hanging-punctuation fix allows ideographic space (U+3000) to hang when used with the first value (revision 308605). These changes improve typographic control, especially for international and quote-heavy content.
4. What editing issues were resolved?
Three key editing problems are fixed. First, the Font Picker style selection no longer becomes unusable after changing fonts when editing multiple lines of text (revision 308562). Second, copying and pasting content across different websites now correctly preserves emoji images instead of losing them (revision 309176). Third, text selection no longer jumps unexpectedly when selecting absolutely-positioned content inside an element with user-select: none (revision 308451). These fixes make text editing more reliable and intuitive in web apps.
5. What fixes were made to forms and HTML parsing?
A frustrating form bug—where keyboard tabbing position was lost when a focused button became disabled, causing focus to jump to the beginning of the page—is now solved (revision 308991). Two HTML parsing issues were also corrected: viewport <meta> now correctly treats form feed as ASCII whitespace per the specification (revision 309044), and pixel-length margin attributes on <body>, <iframe>, and <frame> elements are parsed properly (revision 308526). These ensure better compliance and more predictable layout behavior.
6. What media playback improvements does this release include?
Several media-related bugs have been squashed. Decoding WebM audio files with more than two channels now works (revision 308749). MediaCapabilities.decodingInfo() no longer incorrectly reports VP8 in WebM as unsupported (revision 308789). MP4 files containing Opus audio tracks can now be decoded with decodeAudioData (revision 309140). Live Text selection is now available on paused fullscreen videos (revision 308498). FairPlay-protected VP9 content plays correctly via MediaSource (revision 308622). Autoplay waits for default text tracks to finish loading (revision 308796). The currentTime getter returns defaultPlaybackStartPosition when no media player exists (revision 308654). HTMLMediaElement fires a timeupdate event when resetting playback position during media load (revision 308695). And a fix for the preload attribute was also included. These updates improve audio and video reliability across formats and features.
7. Are there any other noteworthy fixes?
While the changelog focuses on CSS, editing, forms, HTML, and media, there are also behind-the-scenes stability enhancements. The release contains WebKit changes across many areas, ensuring a smoother developer experience. For a complete list, check the WebKit blog or the commit history between revisions 308418 and 309286. Overall, Safari Technology Preview 240 is a solid update for anyone testing cutting-edge web technologies.