Release Notes for Safari Technology Preview 56

Safari Technology Preview Release 56 is now available for download for macOS Sierra and macOS High 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 230913-231553.

This is the last release of Safari Technology Preview that will install and run on macOS Sierra. To continue testing or living on the latest enhancements to Safari and WebKit, please upgrade to macOS High Sierra.


  • Implemented Intl.PluralRules (r231047)


  • Added support for stream APIs (r231194)


  • Fixed event listener removal to be immediate (r231248)
  • Fixed DHTML drag operations to report the number of files in the operation (r231003)
  • Fixed window.postMessage(), window.focus(), and window.blur() unexpectedly throwing a TypeError (r231037)
  • Serialized font-variation-settings with double-quotes to match standards (r231165)
  • Stopped using the id of an <iframe> as fallback if its name attribute is not set (r231456)


  • Added support for the WHATWG proposed From-Origin:same and From-Origin:same-site response headers with nested frame origin checking as an off by default experimental feature (r230968)
  • Fixed CSP referrer for a document blocked due to a violation of its frame-ancestors directive (r231461)
  • Fixed CSP status-code for a document blocked due to a violation of its frame-ancestors directive (r231464)
  • Fixed CSP to pass the document’s referrer (r231445)
  • Fixed CSP to only notify Web Inspector to pause the debugger on the first policy to violate a directive (r231443)
  • Fixed a bug causing first-party cookies to be blocked on redirects (r231008)


  • Fixed CSS filters which reference SVG filters to respect the color-interpolation-filters of the filter (r231473)
  • Fixed feTurbulence to render correctly on a Retina display (r231485)
  • Fixed shape-outside and filter styles occuring twice in the result of getComputedStyle (r230976)


  • Changed font collection fragment identifiers to use PostScript names (r231259)
  • Fixed selecting text on a webpage causing the text vanish (r231178)
  • Fixed hiding then showing an <object> of type image to ensure the underlying image is displayed (r231292)


  • Changed MediaStreams that are playing to allow removing some of its tracks (r231304)
  • Updated text track cue logging to include cue text (r231490)

Web Inspector

  • Improved the user experience in Canvas tab to show progress bars while processing actions in a new recording (r231218)
  • Ensured that tabbing through the last section of rules in the Styles editor wraps back to the first section of rules (r231372)
  • Fixed Console drawer resizing when the console prompt has more than one line of code (r231527)
  • Fixed unsupported properties that sometimes don’t get warnings just after adding them (r231377)
  • Updated the Canvas tab to determine functions by looking at the prototype (r231368)