# Safari Technology Preview 12 Release Notes Preview the latest web technology updates including: JavaScript, Web APIs, Web Inspector, MathML, CSS, Rendering, Accessibility, and Security. ## Overview [Safari Technology Preview](https://webkit.org/blog/6017/introducing-safari-technology-preview/) Release 12 is now [available for download](https://webkit.org/downloads/) for both macOS Sierra betas and OS X El Capitan. If you already have Safari Technology Preview installed, you can update from the Mac App Store’s Updates tab. This release covers WebKit revisions [204289–204876](http://trac.webkit.org/log/?rev=204876&stop_rev=204289&limit=999). This release of Safari Technology Preview will be the last that will install and run on OS X El Capitan 10.11.4 and 10.11.5. To continue testing or living on the latest enhancements to WebKit, please upgrade to OS X El Capitan 10.11.6 or the macOS Sierra betas. ### JavaScript - Added checks for `TypedArray.prototype.slice` to ensure the source and destination have not been detached ([r204868](https://trac.webkit.org/changeset/204868/)) - Added exception handling for `const` variables used in a `for-in` or `for-of` loop ([r204586](https://trac.webkit.org/changeset/204586/)) - Improved the performance of `Array.prototype.map` when used with Arrays ([r204488](https://trac.webkit.org/changeset/204488/)) - Implemented `Object.entries` and `Object.values` from the ES2017 specifications ([r204419](https://trac.webkit.org/changeset/204419/), [r204358](https://trac.webkit.org/changeset/204358/)) - Changed the `line`, `column` and `sourceURL` properties of `Error` to be configurable and writable ([r204663](https://trac.webkit.org/changeset/204663/)) ### Web APIs - Fetch API is enabled by default ([r204705](https://trac.webkit.org/changeset/204705/)) - Updated Resource Timing implementation ([r204736](https://trac.webkit.org/changeset/204736/), [r204641](https://trac.webkit.org/changeset/204641/), [r204429](https://trac.webkit.org/changeset/204429/)) - Aligned `Range.surroundContents()` with the latest DOM specification ([r204390](https://trac.webkit.org/changeset/204390/)) - Added support for `HTMLAreaElement.toString()` ([r204871](https://trac.webkit.org/changeset/204871/)) - Changed the `prefix` properties of `Attr` and `Element` to be read-only ([r204648](https://trac.webkit.org/changeset/204648/)) - Changed `` to an `HTMLUnknownElement` and `` to an `HTMLElement` ([r204647](https://trac.webkit.org/changeset/204647/)) - Moved the `prefix`, `namespaceURI`, and `localName` attributes from `Node` to `Attr` and `Element` ([r204624](https://trac.webkit.org/changeset/204624/)) - Aligned text encoding labels with the Encoding specification ([r204605](https://trac.webkit.org/changeset/204605/)) - Added `Animatable`, `AnimationEffect`, `KeyframeEffect` and `Animation` interfaces for Web Animations ([r204594](https://trac.webkit.org/changeset/204594/)) - Aligned `isDefaultNamespace()`, `lookupPrefix()`, and `lookupNamespaceURI()` with the specification ([r204536](https://trac.webkit.org/changeset/204536/)) - Changed `querySelector()` and `querySelectorAll()` to always throw a `SyntaxError` when failing to parse a selector string ([r204522](https://trac.webkit.org/changeset/204522/)) - Moved `embeds`, `plugins`, and `scripts` attributes from `HTMLDocument` to `Document` ([r204450](https://trac.webkit.org/changeset/204450/)) - Moved the `compatMode` and `designMode` properties from `HTMLDocument` to `Document` ([r204451](https://trac.webkit.org/changeset/204451/), [r204449](https://trac.webkit.org/changeset/204449/)) - Updated `getElementsByTagName()` to take a qualified name parameter ([r204441](https://trac.webkit.org/changeset/204441/)) - Exposed `crypto.getRandomValues` to Web Workers ([r204481](https://trac.webkit.org/changeset/204481/)) - Added application/vnd.api+json as a valid JSON MIME-type ([r204437](https://trac.webkit.org/changeset/204437/)) ### Web Inspector - Added *Open in New Tab*, *Reveal in Resources Tab* and *Copy Link Address* to the context menu of link attributes ([r204846](https://trac.webkit.org/changeset/204846/)) - Added *Download File* context menu item for resource tree elements ([r204862](https://trac.webkit.org/changeset/204862/)) - Added *Copy Selected* context menu item to the Console ([r204511](https://trac.webkit.org/changeset/204511/)) - Added a visual editor for the `spring()` timing-function ([r204775](https://trac.webkit.org/changeset/204775/)) - Fixed an issue where “NaN x NaN” was shown for invisible elements in the *Styles → Computed → Box Model* section ([r204759](https://trac.webkit.org/changeset/204759/)) - Set Open Resource Dialog to jump to the last line when the specified line number (“:n”) is more than the total line count of the resource ([r204755](https://trac.webkit.org/changeset/204755/)) - Added an icon for selectors that only affect pseudo-elements ([r204754](https://trac.webkit.org/changeset/204754/)) - Fixed DOM nodes shifting when hovering over them in the Console ([r204520](https://trac.webkit.org/changeset/204520/)) - Fixed the alignment of the Close button of the selected item in the Network tab ([r204491](https://trac.webkit.org/changeset/204491/)) - Changed the Visual Styles Sidebar behavior for SVGs to show SVG specific sections ([r204758](https://trac.webkit.org/changeset/204758/)) - Changed the Visual Styles Sidebar *Text* → *Content* section to only be visible for a pseudo-element ([r204757](https://trac.webkit.org/changeset/204757/)) - Escaped *Text → Content* in the Visual Styles Sidebar ([r204510](https://trac.webkit.org/changeset/204510/)) - Addressed status icons flickering from rapid updates in the Visual Styles Sidebar ([r204562](https://trac.webkit.org/changeset/204562/)) - Fixed the placement of Error and Warning icons in the Visual Styles Sidebar ([r204490](https://trac.webkit.org/changeset/204490/)) - Fixed a hang when using Command-Shift-O (⌘⇧O) when the loaded web page has frames ([r204428](https://trac.webkit.org/changeset/204428/)) - Enabled editing node attributes, content, and styles for shadow DOM nodes ([r204370](https://trac.webkit.org/changeset/204370/)) - Improved the display of large numbers in the console log counter on the dashboard ([r204642](https://trac.webkit.org/changeset/204642/)) - Improved the display of large class lists and made the quick-toggle easier to discover ([r204496](https://trac.webkit.org/changeset/204496/)) ### MathML - Improved the extraction of operator and token elements’ characters ([r204830](https://trac.webkit.org/changeset/204830/)) - Introduced a `MathMLRowElement` class for `mrow`-like elements ([r204779](https://trac.webkit.org/changeset/204779/)) - Introduced a `MathMLAnnotationElement` class for the `` and `` elements ([r204692](https://trac.webkit.org/changeset/204692/)) ### CSS - Enabled the `:host` pseudo-class to style elements in the shadow tree ([r204724](https://trac.webkit.org/changeset/204724/)) - Corrected the namespace prefix handling in front of element name CSS selectors ([r204591](https://trac.webkit.org/changeset/204591/)) ### Rendering - Fixed SVG clip-path to work on a root SVG element ([r204872](https://trac.webkit.org/changeset/204872)) - Fixed `ctx.drawImage` to clip the source rectangle if it is outside the source image ([r204517](https://trac.webkit.org/changeset/204517/)) ### Accessibility - Labelled audio description tracks correctly to prevent user confusion ([r204601](https://trac.webkit.org/changeset/204601/)) - Added a percentage value description for the media control’s timeline slider ([r204361](https://trac.webkit.org/changeset/204361/)) ### Security - Improved `URLParser` parsing IPv4 addresses and URLs without credentials ([r204701](https://trac.webkit.org/changeset/204701/), [r204544](https://trac.webkit.org/changeset/204544/)) - Added support to handle cross-origin redirect requests while in CORS mode ([r204693](https://trac.webkit.org/changeset/204693/), [r204795](https://trac.webkit.org/changeset/204795/)) - Corrected the `Upgrade-Insecure-Request` state handling between navigations ([r204521](https://trac.webkit.org/changeset/204521/)) - Added a sandbox for the Adobe Flash Player ESR plug-in used in enterprise environments ([r204461](https://trac.webkit.org/changeset/204461)) - Changed instantiation of WebKit plug-ins to happen at layout time, instead of at style resolution time ([r204320](https://trac.webkit.org/changeset/204320/)) --- Copyright © 2026 Apple Inc. 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