Release Notes for Safari Technology Preview 27

Safari Technology Preview Release 27 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 213822-214535.

Browser Changes

  • Added a “Reload Page From Origin” alternate menu item to the View menu. This action reloads a page without using cached resources.
  • Removed the Option-Command-R (⌥⌘R) keyboard shortcut from “Enter/Exit Responsive Design Mode” and mapped it to “Reload Page From Origin” instead.
  • Removed the Disable Caches menu item in the Develop menu. The equivalent functionality is now available through Web Inspector’s Network tab.


  • Implemented ESNext Object Spread proposal (r214038)
  • Changed to allow labels named let when parsing a statement in non-strict mode (r213850)
  • Fixed const location = "foo" in a worker to not throw a SyntaxError (r214145)


  • Aligned initEvent, initCustomEvent, initMessageEvent with the latest specification (r213825)
  • Aligned Document.elementFromPoint() with the CSSOM specification (r213836)
  • Changed XMLHttpRequest getAllResponseHeaders() to transform header names to lowercase before sorting (r214252)
  • Fixed sending an empty "Access-Control-Request-Headers" in preflight requests (r214254)
  • Implemented self.origin (r214147)
  • Implemented the “noopener” feature for (r214251)
  • Improved index validation when using uint index values in WebGL (r214086)
  • Prevented beforeunload alerts when the user hasn’t interacted with the web page (r214277)
  • Prevented innerText setter from inserting an empty text node if the value starts with a newline (r214136)
  • Prevented new navigations during document unload (r214365)
  • Prevented WebSQL databases from being openable in private browsing (r214309)
  • Changed serialization of custom properties in longhand to be "", not the value of the shorthand property (r214383)
  • Changed to tear down descendant renderers when a <slot> display value is set to "contents" (r214232)


  • Fixed pausing animated SVG images when they are outside the viewport, or removed from the document (r214503, r214327)
  • Changed asynchronous image decoding to consider when the drawing size is smaller than the size of the image (r213830)
  • Prevented large images from being decoded asynchronously when they are drawn on a canvas (r214450)
  • Fixed the flow state for positioned inline descendants (r214119)
  • Fixed initial letter rendering that follows pagination (r214110)
  • Fixed clipping columns horizontally in multi-column layout (r213832)
  • Fixed animated GIFs that fail to play in multi-column layout (r213826)


  • Fixed an issue where a dynamically applied :empty pseudo class with display:none does not get unapplied (r214290)
  • Unprefixed -webkit-min-content, -webkit-max-content and -webkit-fit-content (r213831)


  • Fixed loading media files in a <video> tag that are served without a filename extension (r214269)
  • Suspended silent videos playback in background tabs to save CPU (r214195)

Web Inspector

  • Added “Disable Caches” toggle in the Network tab that only applies to the inspected page while Web Inspector is open. (r214494)
  • Added “Save Selected” context menu item to Console (r214077)
  • Added RTL support to the Timeline tab (r213925, r213942, r213928, r213997, r213924, r214009, r214062, r214076)
  • Added RTL support for the Find banner (r214048)
  • Added more accurate Resource Timing data in Web Inspector (r213917)
  • Added context menu item to log content of WebSocket frame (r214371)
  • Added icons for SVG Image cluster path components (r214011)
  • Added keyboard shortcut to clear timeline records (r214140)
  • Added a connection indicator for when a WebSocket connection is open or close (r214354)
  • Changed Option-clicking the close tab button to close all other tabs (r214464)
  • Changed to allow the user to copy locked CSS selectors in Style Rules sidebar (r213887)
  • Changed to allow users to click links in inline and user-agent styles (r214366)
  • Changed SVG image content view to allow toggling between the image and source (r213999)
  • Changed Event Listeners detail section to show listeners by element rather than by event (r213874)
  • Changed Event Listeners to add missing ‘once’ and ‘passive’ event listener flags (r213873)
  • Fixed an issue where adding a WebSocket message could change the currently selected resource (r214387)
  • Fixed clicking DOM breakpoint marker to enable and disable breakpoints (r214256)
  • Fixed an exception when clicking on Clear Network Items icon with the timing popover visible (r214199)
  • Fixed local storage keys and values starting with truncated strings (r214308)
  • Fixed empty attributes added to a DOM tree outline element adding whitespace within the tag (r214141)
  • Fixed an exception when fetching computed styles that can break future updates of section (r213961)
  • Fixed syntax highlighting and formatting when inspecting a main resource that is JavaScript or JSON (r214492)
  • Fixed pseudo-class markers overlapping DOM breakpoints and disclosure triangles (r214196)
  • Fixed an issue causing the Resource details sidebar to display previous image metrics when viewing resource where content load failed (r214436)
  • Fixed text selection in the Console to select only message text (r214024)
  • Fixed formatting JSON request data (r214487)
  • Fixed the filename used when saving a resource from the resource image content view (r214133)
  • The file save dialog no longer suggests the top level directory as the default location (r214442)


  • Fixed VoiceOver for editable text on the web (r214112)


  • Added support for SPKI/PKCS8 Elliptic Curve cryptography (r214074)