Release Notes for Safari Technology Preview 28

Safari Technology Preview Release 28 is now available for download for macOS Sierra. If you already have Safari Technology Preview installed, you can update from the Mac App Store’s Updates tab. This release covers WebKit revisions 214535-215271.

Power and Performance

  • Changed to pause silent WebAudio rendering in background tabs (r214721)
  • Changed to pause animated SVG images on pages loaded in the background (r214561)
  • Changed to make inaudible background tabs become eligible for memory kill after 8 minutes (r215077)
  • Changed to kill any WebContent process using over 16 GB of memory (r215055)
  • Throttled DOM Timers to 30fps in cross-origin iframes that the user did not interact with (r215116)
  • Throttled requestAnimationFrame callbacks to 30fps in cross-origin iframes the user did not interact with (r215070, r215153)


  • Adapted content-alignment properties to the new baseline syntax (r214624)
  • Adapted place-content alignment shorthand to the new baseline syntax (r214852)
  • Adapted self-alignment properties to the new baseline syntax (r214564)
  • Fixed scroll offset jumps after a programmatic scroll in an overflow container with scroll snapping (r215075)
  • Implemented the place-items shorthand (r214966)
  • Implemented stroke-color CSS property (r215261)
  • Implemented stroke-miterlimit CSS property (r214787)
  • Unprefixed CSS cursor values grab and grabbing (r215146)


  • Fixed objects with gaps between numerical keys getting filled by NaN values (r214714)
  • Fixed Object.seal() and Object.freeze() on global this (r215072)
  • Fixed String.prototype.replace to correctly apply special replacement parameters when passed a function (r214662)


  • Changed _blank, _self, _parent, and _top browsing context names to be case-insensitive (r214944)
  • Cleaned up touch event handler registration when moving nodes between documents (r214819)
  • Fixed <input type="range"> to prevent breaking all mouse events when changing to disabled while active (r214955)
  • Prevented double downloads of preloaded content from when the content is in MemoryCache (r215229)
  • Fixed WebSocket.send (r215102)

Web Inspector

  • Added a preference for Auto Showing Scope Chain sidebar on pause (r214847)
  • Changed the order of Debugger tab sidebar panels: Scope Chain, Resource, Probes (r215047)
  • Changed XHR breakpoints to be global (r214956)
  • Changed hierarchical path component labels to guess directionality based on content for RTL layout (r214862)
  • Fixed RTL alignment of close button shown while docked (r214902)
  • Fixed RTL layout issues in call frame tree elements and async call stacks (r214846)
  • Fixed RTL layout issues in the debugger dashboard putting arrows on the wrong side (r214899)
  • Fixed RTL layout issues in Type Profiler popovers (r214906)
  • Fixed misplaced highlights in Search results of the Search navigation sidebar for RTL layout (r214864)
  • Fixed disappearing section when clicking on the body of a CSS rule after editing (r214863)
  • Fixed showing indicators for hidden DOM element breakpoints in the Elements tab (r214844)
  • Fixed blank Network tab content view after reload (r214551)
  • Made “Enter Class Name” text field wider so the placeholder text doesn’t clip (r215192)
  • Fixed probe values not showing in the Debugger tab sidebar (r214967)
  • Fixed focusing the Find banner immediately after showing it (r214856)
  • Fixed showing Source Map Resources in the Debugger Sources list (r215082)
  • Fixed Styles sidebar warning icon appearing inside property value text (r214617)
  • Fixed broken tabbing in Styles sidebar when additional “:” and “;” are in the property value (r215170)
  • Fixed clipped data in WebSockets data grid (r215206)
  • Fixed staying scrolled to the bottom as new WebSocket log messages get added (r214587)
  • Included additional pause reason details for DOM “subtree modified” breakpoint (r214861)
  • Included more Network information in Resource Details Sidebar (r214903)
  • Included all headers in the Request Headers section of the Resource details sidebar (r215062)


  • Fixed an issue that prevented non-popup windows from being maximized or resized
  • Fixed an issue that caused previously opened tabs to reopen when Safari was launched in order to run a WebDriver test


  • Exposed a new AXSubrole for the explicit ARIA “group” role (r214623)
  • Fixed VoiceOver web article navigation with an article rotor for sites like Facebook and Twitter (r215236)


  • Fixed seeks to currentTime=0 if currentTime is already 0 (r214959)


  • Fixed clipping across page breaks when including <caption>, <thead> or <tbody> in a <table> (r214712)
  • Fixed Japanese fonts in vertical text to support synthesized italics (r214848)
  • Fixed long Arabic text in ContentEditable with CSS white-space=pre to prevent hangs (r214726)
  • Fixed overly heavy fonts on by attempting to normalize variation ranges (r214585, r214572)


  • Added support for AES-CTR (r215051)


  • Changed private browsing sessions to not look in keychain for client certificates (r215125)


  • Fixed an issue where Safari would throw an exception when evaluating JavaScript ending with an implied return value, where the final statement doesn’t include the return keyword